booklet « controls » - part b quality control of sprayed ... les---b-v... ·...

Version 2013

Booklet

« controls » - part B

Quality control of sprayed concrete

Technical committee Asquapro

ASQUAPRO Technical GuideTechnical GuideTechnical GuideTechnical Guide Booklet «Booklet «Booklet «Booklet « ContrContrContrControls ols ols ols –––– Part BPart BPart BPart B » » » » ---- 2013 2013 2013 2013 versionversionversionversion

ASQUAPRO « Controls - part B » - 2013 version page 2

Controls tests realised on siteControls tests realised on siteControls tests realised on siteControls tests realised on site

Slump test with the Abrams cone (test NF EN 12350-2)

Measurement of the slump with a measuring rod

Injection of a rod Ø 16 in a cone full of concrete

(photo credits: Eric Marsollat)



Realisation of main control tests on site

FOREWORD

As there were a great number of tests to describe, to study and comment on, it was decided to divide the booklet “Controls” into two parts:

• Part A: Issues of the control of sprayed concrete and description of testing methods

• Part B: Realisation of main control tests on site This document is the 2013 version of the booklet “C ontrols”- part B. It replaces the previous version of 2010. It only relates to the operations most usually used on building sites to control the projection quality

⇒ Either during an internal audit which allows the company to make sure – during the works - that it strictly respects the prescriptions of its contract and those of the quality assurance plan.

⇒ Or to carry out the tests on fresh concrete, to take out or spray samples designed for the laboratory tests required for external controls.



TABLE OF CONTENTSTABLE OF CONTENTSTABLE OF CONTENTSTABLE OF CONTENTS

N° de pageN° de pageN° de pageN° de page

FOREWORD ........................................................................................................................3

INTRODUCTION ..................................................................................................................6

REFERENCE DOCUMENTS ...............................................................................................6

DOCUMENTS SPECIFIC TO SPRAYED CONCRETE ....................................................6

“Concrete” standards usable for projection ........ ........................................................7

1 ISSUES OF THE CONTROL OF SPRAYED CONCRETE ......... ..................................9

1.1 CHARACTERISTICS OF IMPLEMENTATION BY PROJECTION ... .....................9

1.1.1 Modification of concrete composition: ............. ..................................................................................9

1.1.2 Presence of fibres ................................. ................................................................................................9

1.1.3 Frameworks coating ................................ .............................................................................................9

2 QUALITY CONTROL CARRIED OUT ON SITE ............... ..........................................10

2.1 Presentation ...................................... .................................................................10

2.2 Test of standard NF P 95 102 ...................... ......................................................10

2.2.1 Realisation of the sprayed samples ................ ..................................................................................10

2.2.1.1 Preparation of the boxes .................................................................................................... 10

2.2.1.2 Projection of the concrete................................................................................................... 11

2.3 Standardised tests specific to sprayed concrete ... ........................................12

2.3.1 NF EN 14488-1 Sampling of hardened and freshly-mixe d concrete ........................................ .....12

2.3.2 NF EN 14488-2 Test of compressive strength at earl y age ............................................. ...............12

2.3.2.1 Tests principle .................................................................................................................... 12

2.3.2.1.1 Driving-in of a needle (test A) ..................................................................................................12

2.3.2.1.2 Driving in and wrenching of a threaded nail (test B) ................................................................13

2.3.3 NF EN 14488-3 Fibre reinforced sprayed concrete: Be nding test on prism ............................... ..13

2.3.3.1 History ................................................................................................................................ 13

2.3.3.2 Preparation of test-tubes on site ........................................................................................ 13

2.3.4 NF EN 14488-4 Test of bond strength by direct tension ........... .....................................................14

2.3.4.1 Taking away of core specimens on site ............................................................................. 14

2.3.5 NF EN 14488-5 energy absorbing capability of a fibre reinforced s lab ........................................16

2.3.5.1 Tests principle .................................................................................................................... 16

2.3.5.2 Preparation of the slabs on site .......................................................................................... 16

2.3.5.2.1 Formwork ................................................................................................................................16

2.3.5.2.2 Projection ................................................................................................................................16

2.3.6 NF EN 14488-6 Measurement of the concrete thickness on a support ........................................17

2.3.7 NF EN 14488-7 fibre content of fibre reinforced co ncrete ............................................ .................18

2.3.7.1 Importance of the test on site ............................................................................................. 18

2.3.7.2 Tests principle .................................................................................................................... 18

2.3.7.2.1 Method A (on hardened concrete) ...........................................................................................18

2.3.7.2.2 Method B (on fresh concrete) ..................................................................................................19

2.4 Standardized tests non-specific to sprayed concrete ....................................20

2.4.1 Tests on fresh concrete .......................... ...........................................................................................20

2.4.1.1 Tests before projection ....................................................................................................... 20

2.4.1.1.1 Dry process: ............................................................................................................................20

2.4.1.1.2 Case of the wet process with dense flow ................................................................................20

2.4.1.1.3 Wet process with diluted flow ..................................................................................................24

2.4.1.2 Tests on fresh concrete after projection ............................................................................. 25

2.4.1.2.1 Dry process .............................................................................................................................25

2.4.1.2.2 Wet process with dense flow ...................................................................................................25

2.4.1.2.3 Wet process with diluted flow ..................................................................................................26



2.4.2. Tests on hardened concrete ........................ ......................................................................................26

2.4.2.1 General points .................................................................................................................... 26

2.4.2.2. Calculation of density NF EN 12390-7 ............................................................................... 26

2.4.2.3 Penetration depth of pressurised water NF EN 12390-8.................................................... 26

2.4.2.4 Determination of rebound number NF EN 12504-2 ........................................................... 27

2.5 Non-standardized tests used for sprayed concrete .. .....................................27

2.5.1 Tests on fresh concrete specific to sprayed concret e ....................................................................27

2.5.1.1 Measurement of density after projection, on fresh concrete .............................................. 27

2.5.1.1.1 Dry process: ............................................................................................................................27

2.5.1.1.2 Wet process: ...........................................................................................................................28

2.5.1.2 Measurement of consistency.............................................................................................. 29

2.5.1.2.1 Dry process: ............................................................................................................................29

2.5.1.2.2 Wet process ............................................................................................................................30

2.5.1.3 Measurement of the water content of the concrete in place .............................................. 31

2.5.1.3.1 Dry process .............................................................................................................................31

2.5.1.3.2 Wet process ............................................................................................................................32

2.5.1.4 Underwater sieving of a sample of concrete in place ......................................................... 32

2.5.1.4.1 Dry process .............................................................................................................................32

2.5.1.4.2 Wet process ............................................................................................................................33

2.5.1.5 Sieve analysis of the residue on a 0.080 mm sieve ........................................................... 33

2.5.2 Tests on fresh concrete non-specific to sprayed co ncrete ............................................ ................34

2.5.2.1 34

2.5.2.1.1 Test using the pallet plasticimeter. ..........................................................................................35

2.5.2.1.2 Pompabilimeters ......................................................................................................................36

2.5.3 Tests on hardened concrete non-specific to sprayed concrete ......................................... ...........37

2.5.3.1 Non-destructive tests on building site ................................................................................. 37

2.5.3.1.1 Sonic echo-sounding with a hammer ......................................................................................37

2.5.3.1.2 Measurements of sclerometric index .......................................................................................41

2.5.4 Tests on hardened concrete specific to sprayed con crete ............................................. ...............43

2.5.4.1 Strength at young ages ...................................................................................................... 43

2.5.4.1.1 "G.I.R” Procedure (Guaranteed Initial Resistance) .................................................................43

3 FREQUENCIES OF THE TESTS AND MEASUREMENTS ......... ..............................45

3.1 INSPECTION CATEGORIES ..............................................................................45

3.2 Table of minimal frequencies ...................... .....................................................45



INTRODUCTION

Thanks to various tests it is currently possible to check some characteristics of freshly-sprayed concrete and the performances of hardened concrete before, during and after works. The tests are divided into: � internal audits carried out by the company according to methods and frequencies

described in its Quality Assurance Plan. � external audits carried out either by an entity of the company, separate from the works,

or by an external organisation paid by the company. � external audits carried out by an independent organisation paid by the contractor.

REFERENCE DOCUMENTS

This part B of the booklet “Controls” of the Asquapro guide refers to the standards or recommendations in force. For dated references, only the dated edition applies. For undated references it is the last known edition which is taken into account.

DOCUMENTS SPECIFIC TO SPRAYED CONCRETEDOCUMENTS SPECIFIC TO SPRAYED CONCRETEDOCUMENTS SPECIFIC TO SPRAYED CONCRETEDOCUMENTS SPECIFIC TO SPRAYED CONCRETE

Afnor standard: NF P 95-102 April 2002 Civil engineering works Repair and reinforcement of concrete and masonry - sprayed concrete Specifications relating to the technique and materials used

This standard is not in contradiction with the standards NF EN hereafter. It gives very useful information on the

grading curves of the mixtures which do not appear in the NF EN 14487-1. It thus is still used. Standardized tests (NF EN & EN) NF EN 14487-1 March 2006 Sprayed concrete

Part 1: Definitions, specifications and conformity NF EN 14487-2 April 2006 Sprayed concrete

Part 2: Implementation NF EN 14488-1 October 2005 Tests for sprayed concrete

Part 1 sampling of hardened and fresh concrete NF EN 14488-2 October 2006 Tests for sprayed concrete

Part 2: compressive strength of sprayed concrete at early age



NF EN 14488-3 July 2006 Tests for sprayed concrete

Part 3: bending strengths (at first peak, last and residual)

of plane-parallel core samples made of fibre reinforced concrete NF EN 14488-4 October 05 Tests for sprayed concrete

Part 4: Bond strength of cores by direct tension NF EN 14488-5 July 2006 Tests for sprayed concrete

Part 5: determination of the energy absorption capacity of a

fibre reinforced slab specimen June 2006 Tests for sprayed concrete

Part 6: thickness of concrete on a substrate

NF EN 14488-7 July 2006 Tests for sprayed concrete

Part 7: fibre content of fibre reinforced concrete

NF EN 934-1 April 2008 Admixtures for concrete, mortar and grout Part 1: common requirements

NF EN 934-5 December 2007 Admixtures for concrete, mortar and grout Part 5: admixtures for sprayed concrete: definitions, requirements,

conformity, marking and labelling

AFTES recommendations AFTES 1979 Tunnels construction method with immediate support

using sprayed concrete and bolting TOS n°31

AFTES 1993 Sprayed concrete technology and implementation TOS n°117

AFTES 1994 Fibre reinforced sprayed concrete technology and implementation TOS n°126

AFTES 2001 Design and dimensioning of sprayed concrete for underground works TOS n°164

“Concrete” standards usable for projection“Concrete” standards usable for projection“Concrete” standards usable for projection“Concrete” standards usable for projection

European standards approved by AFNOR (NF EN) NF EN 206–1 April 2004 Concrete Part 1: Specification, performance, production and conformity NF EN 206–1/A1 April 2005 Concrete Part 1: Specification, performance, production and conformity

(amendment 1 to standard NF EN 206-1)

NF EN 206–1/A2 October 2005 Concrete Part 1:

Specification, performance, production and conformity

(amendment 2 to standard NF EN 206-1)

NF EN 206–1/CN December 2012 Concrete Part 1: Specification, performances, production and conformity (national addition to standard

NF EN 206-1)

NF EN 12350-1 Test for fresh concrete Part 1: Sampling April 2012



NF EN 12350-2 Testing fresh concrete Part 2: Slump test April 2012

NF EN 12350-6 Testing fresh concrete Part 6: Density April 2012

NF EN 12350-7 Testing fresh concrete Part 7: Air content, pressure methods April 2012

NF EN 12350-8 Testing fresh concrete Part 8: Slump-flow test Nov. 2010

NF EN 12350-9 Testing fresh concrete Part 9: V-funnel test Nov. 2010

NF EN 12390-5 Testing hardened concrete Part 5: Flexural strength of test specimens April 2012

NF EN 12390-7 Testing hardened concrete Part 7: Density Sept. 2001 NF EN 12390-8 Testing hardened concrete Part 8: Depth of penetration of water under pressure

April 2012

NF EN 14889-1 Fibres for concrete Part 1: steel fibres

Definitions, specifications and conformity Nov. 2006

NF EN 14889-2 Fibres for concrete Part 2: polymer fibres

Definitions, specifications and conformity Nov. 2006

NF EN 12504-1 Testing concrete in structures Part 1 : cored specimens

Taking out, examining and testing

compressive strength April 2012

NON “NF EN” STANDARDIZED TESTS BUT USABLE FOR SPRAY ED CONCRETE Measurement of water content of fresh concrete after projection Measurement of cement and fines content of fresh concrete after projection Measurement of fresh concrete consistency after projection (dry process) with a penetrometer Estimating fresh concrete consistency using the appropriate tool (wet process) Hammer testing on hardened concrete to control the adhesion to the substrate



1 ISSUES OF THE CONTROL OF SPRAYED CONCRETE

This subject was covered in the booklet “Controls” – part A, Chapter 1, so please refer to it to obtain all the details on the reasons that led to the development of particular testing methods. We point out hereafter only the main characteristics of implementation.

1.11.11.11.1 CHARACTERISTICS OF IMPLEMENTATION BY CHARACTERISTICS OF IMPLEMENTATION BY CHARACTERISTICS OF IMPLEMENTATION BY CHARACTERISTICS OF IMPLEMENTATION BY

PROJECTIONPROJECTIONPROJECTIONPROJECTION

1.1.1 Modification of concrete composition

As there is a loss of aggregates by rebound, the projection by dry process increases the cement content of the concrete in place and consequently its resistance. The increase of the cement content is small, or even non-existent when in wet process, but nevertheless the projection modifies the composition because of the compaction by the hammering of the aggregates, just like during the dry process. The composition of the concrete in place being therefore different from that of the mixture introduced into the machine, it is essential to manufacture or to take the samples designed for the tests directly from sprayed concrete because the fabrication of samples or concrete test-tubes poured in moulds would not be representative.

1.1.2 Presence of fibres

The projection of concrete always being done towards a wall (structure, formwork, rock…), the positioning of the fibres (whatever their nature) inside the sprayed concrete is not completely random. The fibres indeed tend to go in successive plans, parallel to the wall but in a random way in each one of these plans.

1.1.3 Frameworks coating

Projection generating a “shade effect” likely to involve the creation of empty spaces behind the steel bars, it is necessary to control the good coating of the frameworks. To make sure there are no empty space behind the steels, the solution which would consist in taking core samples crossing concrete and frameworks layers cannot obviously be considered as a control method for a structure under mechanical stress. This solution can however be employed on “test slabs” or experimental works. Apart from these circumstances and as long as there is no reliable non-destructive test, the only currently available mean to control the coating is to check before the works the qualification of the nozzlemen through practical tests, and during the works, to follow-up the projection visually.



2 QUALITY CONTROLS CARRIED OUT ON SITE

2.12.12.12.1 PresentationPresentationPresentationPresentation

The testing methods, standardized or not, usable to control the quality of sprayed concrete, were briefly described in the booklet “Controls” – part A. Only the operations that will be carried out on sit es by the companies, the laboratories or design departments, are the subject of this part B . To facilitate the navigation between the parts A and B of the booklet “Controls”, the various “on site” operations will be examined in the same order as that of the classification of the tests descriptions in the part A. Namely:

� Standardized tests specific to sprayed concrete � Standardized tests non-specific to sprayed concrete � Non-standardized tests used for sprayed concrete

Standard NF P 95-102 used in France is not removed yet. In addition, it is not in contradiction with standard NF EN 14487-1. The compressive strength test is the only test which it prescribes; it could thus be preserved because it is usable while respecting the European standard. As in part A, it is thus the first examined.

2.22.22.22.2 Test of standard NF P 95 102Test of standard NF P 95 102Test of standard NF P 95 102Test of standard NF P 95 102

This test is intended to measure the compressive strength of the concrete on test-tubes cored out from samples sprayed in boxes before or during the works. The dimensions of the boxes, the coring zones and the dimensions of the core specimens are described in the booklet “Controls” - Part A. Please refer to this booklet. 2.2.1 Realisation of the sprayed samples 2.2.1.12.2.1.12.2.1.12.2.1.1 Preparation ofPreparation ofPreparation ofPreparation of the boxesthe boxesthe boxesthe boxes When the boxes are prepared on site, they are generally entirely made of wood. For projection by dry process, the edges can be open in order not to trap the losses (see picture on the following page). If boxes made of plastic, sheet metal or another material are used, a wood plate must be placed on the bottom where the concrete will be sprayed.



2.2.1.22.2.1.22.2.1.22.2.1.2 Projection of concreteProjection of concreteProjection of concreteProjection of concrete The concrete must be sprayed in the boxes, under conditions rigorously identical to those of the works (personnel, components and equipment). The projection is done on a 15 cm thickness in the coring zone perpendicular to the bottom of the box placed vertically or with an inclination angle of less than 20°. This position of the box cannot be respected when a concrete without accelerating admixture is sprayed by wet process. In this case, it is authorised to place the box horizontally. The projection distance of 1 metre, given as an indication in the standard, can be reduced to approach the real distance on site when for example the projection must be done in a very narrow gallery. Conversely, when large flow machines are used, the test must be carried out with the same projection distance as the one used on site.

Example of projection by dry process of a concrete with an accelerating admixture, in an AFNOR type box with open sides.



2.32.32.32.3 StandardStandardStandardStandardised tests specific to sprayed concreteised tests specific to sprayed concreteised tests specific to sprayed concreteised tests specific to sprayed concrete

2.3.1 NF EN 14488-1 Sampling of hardened and freshly-mixed

concrete

This sampling which constitutes the part 1 of the standard EN 14488, directly relates to the AFNOR test previously described for which it was noticed that the box dimensions (0.25 m2 with small side ≥ 0.40 m) were complying with the regulations of the new standard and could thus be kept for manual projection. Concerning the dimensions of the core specimens, the standard 14488-1 does not give any indication. It is necessary to consult the standard NF EN 14487-1 to find that “their minimal diameter must be 50 mm and the ratio height/diameter must be equal to 1 or 2”. These indications are less demanding than the French (core specimen Ø 60 mm with a slenderness ratio of 2) Given the number of tests carried out in France since 1972 on core specimens Ø 60 mm with a slenderness ratio of 2, it is recommended when it is possible, to keep these dimensions. But if it is necessary, they can be reduced to Ø 50 mm with a slenderness ratio of 1, while respecting the standard NF EN 14487-1. The standard 14488-1 keeps the French regulations about the installation of the box at less than 20° from the vertical but does not take account of the fact that this requirement cannot be met if a fluid concrete without accelerating admixture is sprayed by wet process. As the problem is not solved yet, the comment made in paragraph 2.2.1.2 (in bold italics) of the present document remains valid.

2.3.2 NF EN 14488-2 Test of compressive strength at early age

2.3.22.3.22.3.22.3.2.1.1.1.1 Tests principleTests principleTests principleTests principle These tests are carried out on sites but require a specific equipment which should be used only by engineers or technicians applying the procedures described in the standard. For large sites, the equipment can be on the site and used by the personnel of the company for internal audits, but generally these tests are realised by an external laboratory. The standard plans 2 tests:

• Test A for very young concrete (strength from 0.2 to 1.2 MPa) • Test B for older concrete (strength from 3 to 16 MPa)

2.3.2.1.1 Driving-in of a needle (test A)

This test measures the necessary strength to have a needle penetrate into young concrete. It is very useful on site because it measures the compressive strength of a very young concrete in a few minutes. The value of the reaction strength gives an estimate of the compressive strength from a conversion curve.



2.3.2.1.2 Driving in and wrenching of a threaded na il (test B)

This test measures the strength necessary to tear off a nail inserted beforehand in a concrete whose resistance is higher than that of test A, which was generally practised on this same sprayed concrete when it was younger.

2.3.3 NF EN 14488-3 Fibre reinforced sprayed concrete:

Bending test on prism

2.3.3.12.3.3.12.3.3.12.3.3.1 HistoryHistoryHistoryHistory

Behaviour tests on prismatic test-tubes subjected to bending tests were initially developed in Japan in 1984 (JSCE-SF4), in the USA in 1989 (test ASTM C1018-89) and in France in 1993 (NF P 18409). At the beginning, these tests were designed for poured fibre concretes but they were quickly adapted to sprayed concretes simply by sawing out test-tubes from sprayed slabs. In Sweden a test was developed especially for fibre reinforced sprayed concretes. This test (bending – 4 points) is similar to the French test of 1993, even regarding the specimen dimensions, but in addition it includes an evaluation of ductility by examination of successive residual strengths. This Swedish test was used to develop the standard EN 14488-3. 2.3.3.22.3.3.22.3.3.22.3.3.2 Preparation of testPreparation of testPreparation of testPreparation of test----tubes on sitetubes on sitetubes on sitetubes on site The standard indicates that the test-tubes (75 mm height, 125 mm width and at least 500 mm length) are sawn out in a laboratory from a sample sprayed on site, in a non-absorbent box. On site, the boxes must have sufficient dimensions so that the slabs obtained after removal of the formwork allow to saw out 3 test-tubes (boxes approx. 500 mm x 700 mm and 100 mm thick can be appropriate). The projection quality is very important: it must be carried out in the presence of a person in charge for external control, or if not, by a person in charge of the internal audit. This projection must be carried out by the certified operators in charge of the works, with the materials and equipment that will be used (in the case of suitability tests) or that are used (in the case of control tests). The nozzleman must take time to regulate the supply of water at the nozzle to obtain the desired consistency before spraying in the box. He must then start with the edges (see picture) and do his utmost not to trap losses in the slab.



The indications about the installation of the box to less than 20 degrees of the vertical plane as for the NF EN 14888-1 and listed in paragraph 2.3.1, apply only for concretes (with or without accelerating admixture) sprayed by dry process, as well as for concretes with accelerating admixture sprayed by wet process. As it was indicated in paragraph 2.2.1.2, these indications cannot apply when a concrete without accelerating admixture is sprayed by wet process; in this case the box is placed horizontally. In any case, the sample should not be sent to the laboratory during the first 48 hours. At the laboratory, the test-tubes are sawn to the prescribed dimensions (125 x 75 x 500) to be tested. The moulded lower faces are those to be put under stress.

2.3.4 NF EN 14488-4 Test of bond strength by direct tension

The in situ test uses a tripod traction device with a bellows jack which is described in standard NF P 18-858 to test repair products applied in low thickness on a poured reference concrete. This test was initially used. This test quickly appeared not to be appropriate to measure the adhesion of a concrete often sprayed in a 10cm thick layer on a substrate hardly ever flat. The standard NF EN 14488-4 that we are examining only relates to the direct tensile test realised in a laboratory on specimens taken from th e structure. Therefore, the in situ test should not be prescribe d any more. 2.3.4.12.3.4.12.3.4.12.3.4.1 Taking away of core specimens on siteTaking away of core specimens on siteTaking away of core specimens on siteTaking away of core specimens on site The quality of this on site operation is by far the most delicate and important operation of the test. Unlike the part carried out in laboratory with the equipment required by the standard and according to the prescribed procedure, there exist indeed little or no recommendations concerning the extraction of core samples on site. It often happened that operators, even coming from considered laboratories, have neither the adapted equipment nor the know-how. It is thus recommended to the company that the person in charge of the internal audit checks that the extractions are correctly carried out; indeed a building site can be stopped because of an extraction badly done. The technician of the company in charge of the verification of the core specimen extraction must make sure that:

• The core drill and the corer are in good condition (no play and projecting diamonds) • the core drill is perfectly fixed by an expansion anchor blocked in a hole Ø ≥ 15 mm

and provided with a clamping screw. • the extraction is made with a sufficient water injection (pressure and flow) • the progress of the manually driven corer is quite regular • the depth of the extraction is sufficient (see below) • the extraction of the core specimen is done carefully.



As the standard recommends that the test-tubes subjected to traction have a diameter “d” from 50 to 100 mm and that their length is equal to 2d, the overall length of the core specimen must definitely be higher than 2d. Indeed, the technician of the laboratory must be able to recut transversely each specimen at both ends so that the adhesion zone is as close as possible to the middle of the test-tube. The technician of the company must thus check that the specimens have the right length and especially that the part drilled in the support is quite sufficient. He must mark the specimens with indelible ink and can also photograph them. The setting of the specimens in boxes is generally made by the technician of the laboratory.

Coring in a tunnel vault to control the adhesion in direct traction (photo credits: C. Resse) Pneumatic machine (allowing the coring in ceilings)

Fixing of the base by an expansion anchor with threaded rod and nut 2.3.4.2 Laboratory testing For information, at the laboratory steel tablets with a diameter equal to that of the specimen (± 1 mm) are stuck on the 2 modified ends and the test-tube is subjected to an increasing traction until it breaks. All details on the testing machine, the steel tablets and their sticking, the tolerances of the specimens and their conservation, as well as on the results and the test report, are described in the standard NF EN 14488-4. The laboratory must scrupulously apply the recommendations of this standard. It is obvious that the critical point of the test is during the extractions on the site.



2.3.5 NF EN 14488-5 energy absorbing capability of a fibre reinforced slab

For the control of fibre reinforced sprayed concrete, this French test developed and called “bending test centred on slab” by the SNCF, is much more used in France than the bending test on a prism described in the paragraph 2.3.3. This test had indeed been adopted by many European countries well before it was standardized by the European Commission, and then that it acquired the statute of French standard NF EN in July 2006. 2.3.5.12.3.5.12.3.5.12.3.5.1 Test principleTest principleTest principleTest principle A fibre reinforced slab 600 x 600 x 100 mm, sprayed in accordance with the standard NF EN 14488-1 is subjected to a load via a rigid steel square block (100 x 100mm) placed at the centre of the slab. The deformation is measured. The surface located under the curve loads-deformations between 0 and 25 mm indicates the energy (in joules) absorbed during the test to obtain this deformation. 2.3.5.22.3.5.22.3.5.22.3.5.2 PrepaPrepaPrepaPreparation of the slabs on siteration of the slabs on siteration of the slabs on siteration of the slabs on site

2.3.5.2.1 Formwork

Boxes of inner size 600 X 600 X 100 mm must be made with 15 mm minimal thickness plywood (CTBX or bakelised formwork). Unlike the tests of the standard NF EN 14488-1 (see paragraph 2.3.1) for which the boxes sides can be open (because the test-tubes are the core specimens), it is the whole slab that constitutes the sample tested by the laboratory this time. The standard indicates that the thickness of the slab must be of 100 + 0 to 5 mm once recut with the ruler immediately after projection. Although it is not indicated in the standard, this tolerance of 0 to + 5 mm can also be applied to the sides of the boxes used as formworks.

2.3.5.2.2 Projection

The projection quality being very important, the process must be carried out in the presence of a person in charge for external control or if not, by the person in charge for the internal audit. This projection must be carried out by the certified operators in charge of the works, with the materials and equipment that will be used (in the case of suitability tests) or that are used (in the case of control tests). When the projection is made by dry process, the nozzleman must take time to regulate the supply of water at the nozzle to obtain the desired consistency before spraying in the box.



He must then start with the edges (see picture) and do his utmost not to trap losses in the slab. The indication for the installation of the box at less than 20 degrees of the vertical plane as for the standard NF EN 14888-1 and quoted in paragraph 2.3.1, applies. Please remind that this indication is applicable only for concretes (with or without accelerating admixture) sprayed by dry process as well as for concretes with accelerating admixture sprayed by wet process. On the other hand, as it was indicated in paragraph 2.2.1.2, this indication cannot apply when a concrete without accelerating admixture is sprayed by wet process; in this case the box is placed horizontally. The sample should not be sent to the laboratory during the first 48 hours.

Projection by dry process in a box 600 x 600 x 100 for the test NF EN 14888-5 (photo credits: VNF)

2.3.6 NF EN 14488-6 Measurement of the concrete thickness on a

support

This standard aims only to describe a reference procedure to carry out the measurement of the sprayed thickness. It prescribes: For fresh concrete, that is to say during projection (or some seconds after in the case of a concrete with an accelerating admixture), insert a depth gauge in the sprayed concrete in order to measure its thickness.



For hardened concrete, bore holes or core the concrete down to the substrate, then “the depth of the holes or the length of the extracted specimens is measured”. It is recommended to drill 5 holes separated by 600 ± 50 mm on 2 perpendicular lines or to take off specimens according to the same diagram.

2.3.7 NF EN 14488-7 fibre content of fibre reinforced concrete

2.3.7.12.3.7.12.3.7.12.3.7.1 Importance of the test on siteImportance of the test on siteImportance of the test on siteImportance of the test on site We know that the fibre content of the concrete in place can be very different from the proportion recommended for the basic mixture. It is therefore necessary to know this content from the moment of projection to avoid disappointments when receiving the results of the tests on hardened concrete (especially for the standards NF EN 14488-3 and NF EN 14488-5 described in paragraphs 2.3.3. and 2.3.5). The measurement of the fibre content of hardened concrete cannot be made at the moment of projection, in consequence it is not of same interest – as an “alarm signal” - as the measurement on fresh concrete. It can however be useful when tests on fresh concrete were not done and that test results at 28 days on prisms or slabs are not satisfactory. The measurement on fresh concretes (see method B be low) is of greatest interest and must thus preferably be prescribed. 2.3.72.3.72.3.72.3.7.2.2.2.2 Test principleTest principleTest principleTest principle “The fibres are extracted from a sample of hardened concrete (method A) or of fresh concrete (method B). The fibre content is measured from their mass and the volume of the concrete sample” (article 3 of the standard NF EN 14488-7).

2.3.7.2.1 Method A (hardened concrete)

For this method, only the extractions must be made on site, taking all the precautions described previously to carry them out. (see paragraph 2.3.4.1). Three specimens with a diameter between 50 and 100 mm must be taken from the in situ concrete or from a test slab. Their volume is calculated in the laboratory, considering their dimensions measured or by weighing in the water in accordance with EN 12350-6. Each specimen is then crushed until complete disintegration to separate the fibres from concrete, to collect and to weigh them.



2.3.7.2.2 Method B (fresh concrete)

Three samples from 1 to 2 kg are cut out with a trowel, in situ or in a test slab. Their volume is determined by weighing in the air and then in water (EN 12390-7). The density of the wet sample is then calculated. The fibres are withdrawn from the sample by washing on a sieve. For synthetic fibres, the sample can be soaked with alcohol and stirred until the fibres float on the surface. For some of these fibres, as the polypropylene fibres which density is lower than 1, the sample is plunged in water. Then the fibres must be dried, cleaned and weighed to the nearest 0.1 g for steel fibres or to the nearest 0.01 g for polymer fibres. These processes can be carried out on site only by technicians provided with a laboratory equipment. An easier but not standardized method can nevertheless be used when no equipment for hydrostatic weighing is available on site. Given the fact that it is important to know the in situ fibre content at the time of projection, this method is commonly used on French building sites. The fibres are recovered and weighed in the air and their weight compared with that of the sample. If fresh concrete density is measured after projection, or if the volume of the sample is known geometrically, it is possible to calculate the fibre content per cubic metre in place. These methods are described in paragraph 2.5.1 (see in particular paragraph 2.5.1.1. c)



2.42.42.42.4 Standardized tests nonStandardized tests nonStandardized tests nonStandardized tests non----specific to sprayed concretespecific to sprayed concretespecific to sprayed concretespecific to sprayed concrete

As it was underlined in the booklet “Controls" - part A, tests which have existed for many years to measure and control some characteristics of poured concretes can be used for sprayed concretes without adaptation. It is the case for example of the slump test NF EN 12350-2 (also called test with Abrams cone). It evaluates the consistency of a fresh concrete that can be used for concrete (fibre reinforced or not) sprayed by wet process . The tests which were not designed at the beginning for sprayed concretes but which can be applied to them are numerous but are far from being all used in France. Only those commonly used on sites and whose regulations refer to the French standards and rules are developed in this booklet.

2.4.1 Tests on fresh concrete

2.4.1.12.4.1.12.4.1.12.4.1.1 Tests before projectionTests before projectionTests before projectionTests before projection

2.4.1.1.1 Dry process

The concrete sprayed by dry process mixes with its dampening water only at the moment of impact of the jet on the substrate. No tests on fresh concrete before projection can th erefore exist for this method. Nevertheless tests can be done on these dry mixtures before projection, for example their sieve analysis (after drying if the mixture contains undried sand), in order to control their conformity with the requests of the project manager.

2.4.1.1.2 Wet process with dense flow

2.4.1.1.2.1 Measurement of water content

With the projection by wet process with dense flow, the water introduced during the mixing cannot flow out when concrete goes through the pump or the transfer pipe. Thus, almost all the water remains in the concrete in place. The only water loss due to a possible vaporization between the nozzle and the receiving surface can be regarded as negligible. The concrete water content could be measured before as well as after projection but currently there is no standardized method to take this measure on sites. The only interest of this measurement could be to check, for example upon arrival of a concrete mixer truck, the conformity of the delivered concrete with the regulations, but for this the slump test (NF EN 12350-2, see paragraph 2.4.1.1.2.3 hereafter) is sufficient.



2.4.1.1.2.2 Measurement of density

Before projection, this measure can be taken by complying completely with the requirements of the standardized test NF EN 12350-6, on a sample of at least 5 dm3 taken out before the pumping and compacted by vibration or manually, according to the standard. However, referring to the foreword of this standard which specifies that “a smaller volume can be appropriate for the production control tests” and considering the fact that the grain size of sprayed concretes is generally smaller than poured concretes’, a minimal volume of 2 dm3 could be recommended for sprayed concretes. And yet, this laboratory test (nevertheless feasible on site) is generally not prescribed to evaluate the density of a sprayed concrete, even with this reduced volume of 2 dm3.

2.4.1.1.2.3 Slump test NF EN 12350-2

The standardized test for fresh concrete most employed on French sites is by far the measurement of consistency with an Abrams cone. The main objective of this test is to check that the consistency grade of the concrete delivered and ready to be sprayed is in conformity with the regulations given by the project manager. For projection by wet process with dense flow, the slump test gives one more useful indication on the pumpability of the concrete deliv ered on site. The test is easy to carry out and its results values are trustful: these points largely contributed to its development and its durability. It is practised on a sample taken from the place the concrete is delivered (exit of concrete mixer, dumper, ready-mix plant skip or drum). The equipment necessary for the test includes a flat and rigid basic plate (generally steel plate) that lays on the ground so that it is horizontal. The cone provided with handles is fixed on it. The concrete is then introduced into the cone. It is compacted by tamping in compliance with the requirements of standard NF EN 12350-2 (filling in 3 layers, each of them receiving 25 strokes of a tamping rod Ø 16 mm). For the release from the mould, the cone must be pulled up in a constant way, in 5 to 10 seconds, without any twisting or lateral movement. And finally, the slump is measured to the closest centimetre. A measuring rod is used if the device is equipped with it, otherwise an horizontal ruler is laid (a spirit level for example) on the 30 cm high mould placed on the plate. Then the vertical distance between the higher part of the concrete cone and the horizontal ruler is measured (see pictures of the following page). As an indication, we can consider that for a slump lower than 8 cm, the pumpability is very uncertain. CR: Please give your own opinion on this value



Slump test with the Abrams cone (test NF EN 12350-2)

Tamping rod Ø 16 in the cone filled with concrete

Measurement of slump with the measuring rod

(Photo credits Eric Marsollat)

Measurement without measuring rod but with the tamp ing rod placed on the cone

(photo credit Claude Resse)



Slump-flow test with the Abrams cone NF EN 12350-8 (self-placing concretes)

This test, designed for self-placing concretes, has been approved in November 2010. It was mentioned in the booklet “Controls” part A because it can be used as a test on fresh concrete. It enables to check the conformity of the delivered concrete with the requirements of the project manager and to evaluate its pumpability before being introduced into the spraying machine. This test is quite simple to carry out on site: it uses the same Abrams cone as the one for the test 12350-2. Only the bottom plate is different but it can possibly be made on site (see below).

Equipment:

It is based on the equipment for the slump test NF EN 12350-2 previously described and modified as follows: - the bottom plate is larger (900 x 900mm) in order not to constrain the spreading of the

concrete - the centre of this plate must be marked with a cross and two circles (Ø 210 mm and Ø

500 mm) centred on the cross. - If the test is carried out by only one person, the cone can be ballasted by a steel collar

weighing more than 9 kg around the cone. If there is no collar, an assistant can help to prevent the cone from going up during its loading.

- A chronometer is also necessary.

Test principle

The cone is filled with fresh concrete all at one time, without pricking. It is given a pause for 30 seconds maximum and then the time (t500) is measured from the moment the cone is beginning to be pulled off until the first contact of the concrete with the circle Ø500 mm. Then the largest diameter (dm) of the spread and the one (dr) at 90° of dm are measured. The spread SF is the average (dm + dr) / 2.

Feasibility test for the projection by wet process

It would be very useful to try out the test on one or more sites of projection by wet process, first to confirm that it is feasible with concretes consistencies allowing projection by wet process with dense flow. Then it will be possible to decide if the slump-flow test for self-placing concretes must be prescribed for sprayed concretes, on account of: - its ease of use on site - the additional information it can bring compared to the other tests “standardized and

non-specific to sprayed concrete” described in this article 2.4 and relating to the tests on fresh concrete before projection.



2.4.1.1.2.5 Flow table test NF EN 12350-5

The vibrating table is more cumbersome than the Abrams cone, and therefore less appropriate for on-site controls than the test NF EN 12350-2 for the measurement of slump or the test NF EN 12350-8 for the measurement of spread. The project managers should not thus prescribe its use for controls any more.

2.4.1.1.2.6 V-funnel test NF EN 12350-9 (self-placi ng concrete)

This test is extremely simple to carry out on site. Among the new standardized tests for self-placing concretes, it is certainly the best able to evaluate the pumpability of a fibreless concrete to be projected by wet process with dense flow. The suppliers and users of sprayed concrete reinforced by steel of synthetic fibres think however that the V-funnel should not be used for fibre reinforced sprayed concretes because the fibres can obstruct the flow at the bottom of the V. Nevertheless the test might be feasible with synthetic microfibres. This could be checked in addition to a slump-flow test NF EN 12350-8 for example. The test requires a V-shaped funnel using the same principle as the “Marsh cone” that is used for the measurement of viscosity of cement grouts but having an exit of greater section allowing a fluid mixture to be spread to pass through. To carry out this experimentation, a V-shaped funnel in conformity with the standard (currently on the market), a 12 litres container able to contain the sample intended for the test and a chronometer are all that are needed. Then the test must comply with the recommended procedure.

2.4.1.1.3 Wet process with diluted flow


Contrary to what was written about projection by wet process with dense flow, a considerable part of the water introduced during the mixing can be vaporized during the transit of the concrete in the transfer pipe. As the measurement of the water content before projection is useless, there is no standardized method to take this measure for sprayed concrete.



2.4.1.22.4.1.22.4.1.22.4.1.2 Tests on fresh concrete after projectionTests on fresh concrete after projectionTests on fresh concrete after projectionTests on fresh concrete after projection


With this method, the fresh concrete formed on its substrate has rheological (consistency) and physical (density, compactedness…) characteristics due to the implementation mode. The standardized tests to measure consistency, compactedness and density are all carried out after an extraction from fresh concrete followed by an introduction in a container by tamping or vibration. In consequence, they cannot be used because with the dry process, the characteristics of the concrete altered by the extraction carried out after projection, either on the work or in a vat, would be obligatorily different from those of the concrete implemented by projection. So there is currently no standardized test applicab le to fresh concrete implemented by projection by dry process.

2.4.1.2.2 Wet process with dense flow

2.4.1.2.2.1 General points

All the standardized tests concerning the tests before projection by wet process with dense flow that were quoted in paragraph 2.4.1.1.2., can be carried out after projection if they are useful and were required. Only the place of the extraction after projection is different since it must be made in the freshly-sprayed concrete, either on the work or in a sample tray. The quantity of concrete necessary to the realisation of the test must simply be taken with a shovel or a scoop instead of being collected by gravity out of a concrete-mixer, a concrete mixer truck or a spraying machine.


Like it was written for the tests on fresh concrete before projection, as the loss of water due to a vaporisation between the nozzle and the receiving wall can be regarded as negligible, the measurement of the water content after projection is not of interest.

2.4.1.2.2.3 Measurement of density

This measure can be taken completely complying with the requiremenst of the standardized test NF EN 12350-6, on a sample of at least 5 dm3 taken out after projection on the work or in a box, and compacted by vibration or manually, according to the standard. However, as it was written for the tests on fresh concrete before projection, a minimal volume of 2 dm3 could be recommended. And yet, this laboratory test feasible on site is generally not prescribed to evaluate the density of a sprayed concrete.



2.4.1.2.3 Wet process with diluted flow

As projection by wet process with diluted flow decreases the water content and strongly influences the compactedness and the content of entrained air, it can be useful to consider the modifications brought by the projection. The standardized tests which can inform about the modifications after projection are: � the slump test to compare the consistencies before and afterwards � the measurement of the content of entrained air to know if the required quantity is

respected in the concrete in place, with respect to the resistances freeze-thaw.

2.4.2. Tests on hardened concrete

2.4.2.12.4.2.12.4.2.12.4.2.1 General pointsGeneral pointsGeneral pointsGeneral points Whatever the projection method (dry or wet process), all the standardized tests applying to cast concretes can be used for sprayed concretes as from the moment when it is possible to core out or saw out from sprayed samples, or also to extract (destructive) from the work the test-tubes with the same dimensions as those prescribed in the standards of the tests for cast concrete (with the same tolerances). For example, the bending strength of a prismatic test-tube can be measured by using one of the 2 tests described in the standard NF EN 12390-5. Other tests non-specific to projection can be carried out on hardened sprayed concrete, for example: 2.4.2.2.2.4.2.2.2.4.2.2.2.4.2.2. Calculation of density NF EN 12390Calculation of density NF EN 12390Calculation of density NF EN 12390Calculation of density NF EN 12390----7777 This calculation is made in a laboratory, based on the real measured dimensions or by the measure of water level difference as indicated in the standard. 2.4.2.32.4.2.32.4.2.32.4.2.3 Penetration depth of pressurised water NF EN 12390Penetration depth of pressurised water NF EN 12390Penetration depth of pressurised water NF EN 12390Penetration depth of pressurised water NF EN 12390----8888 This measurement is also done in laboratory on sprayed concrete core specimens, taken in situ or from a box on site.

For this test, the dimensions of the test-tube (150x150 mm for cubes and Ø 150 mm for cylinders) involve the preparation of sprayed concrete samples of unusual size. An adaptation of the testing device must be considered, for example for specimens Ø 100 mm, by noting this deviation from the standard in the test report.



2.4.2.42.4.2.42.4.2.42.4.2.4 Determination of the Determination of the Determination of the Determination of the rebound rebound rebound rebound numbernumbernumbernumber NF EN 12504NF EN 12504NF EN 12504NF EN 12504----2222 This time, this test can be entirely carried out on site while respecting all the requirements of the standard. It provides information on the characteristics of the surface in the zone tested with a sclerometer. It cannot replace the strength tests (NF EN 12390-3, 5 and 6).

Equipment: Sclerometer. Its type must be indicated (for example: Schmidt type N)

Procedure: Follow the standard requirements and note the quality of the tested surface (roughness, moisture) and the orientation of the spray (horizontal, at 45°, on a wall or a vault)

2.52.52.52.5 NonNonNonNon----standardized tests used for sprstandardized tests used for sprstandardized tests used for sprstandardized tests used for sprayed concreteayed concreteayed concreteayed concrete

2.5.1 Tests on fresh concrete specific to sprayed concrete

2.52.52.52.5.1.1.1.1.1.1.1.1 Measurement Measurement Measurement Measurement on fresh concrete on fresh concrete on fresh concrete on fresh concrete of density after projectionof density after projectionof density after projectionof density after projection


With this projection method, the compaction due to the hammering of the aggregates is very important. The sample intended for the measurement of density must thus be sprayed: Several methods can be used to prepare this sample: a) By coring it out using a cylindrical sheet metal container, not very deep and with a

cutting edge, that will be pushed in the freshly-sprayed concrete.

This operation unfortunately alters the sample and reduces its compactedness, therefore its density, near the cutting zone. Nevertheless, this test is used especially by the SNCF with a 1 litre container, to measure the in situ fibre content of fibre reinforced sprayed concretes. Given the quoted operational risks, the test can give only an indication with a margin of error up to ± 5%.



b) By taking freshly sprayed concrete directly from the structure, using a trowel.

This operation completely alters the concrete. It is then manually pressed in a resisting and not absorbing container whose volume is known, to reconstitute its compactedness. The packing can be done by layers of 4 to 5 cm using a simple pestle, while trying to obtain in the mould the same consistency as the one measured with the pocket penetrometer on the concrete in place. The same penetrometer is used to control, layer by layer, the compaction resulting from the tamping down. This method is more precise than the previous one although the bleed-through due to the tamping down in the container modifies the aspect of the visible surface of the concrete which looks wetter than on the sprayed facing.

c) By spraying the concrete directly in a container which is not absorbing and resistant

to projection.

To limit the “edge effects” the mould container must be shallow (4 to 5 cm for moulds from 1 to 2 dm3) and the edges can possibly be tilted. With this method, the compaction is well taken into account and the nests of losses in the angles are negligible (even null when the edges are tilted). The volume of the collecting container can be easily determined by weighing to the nearest gram once it is filled with water. The surfacing of the front side is the only difficulty. It must be cut with a beveled levelling ruler moved on the edges of the mould with an alternate shearing motion. The possible wrenchings due to fine gravels or fibres must be filled and smoothed with a trowel. This method is the most accurate.

2.5.1.1.2 Wet process

With this projection method, the compaction due to the hammering of the aggregates is less important than in the dry process but it exists. The sample intended for the measurement of the density must thus also be made by projection but the risk of trapping losses being weak, it becomes possible to spray directly in a 5 dm3container (the exemption for 2 dm3 is not advisable in this case).



In consequence, the testing method can largely be based on the European standard NF EN 12350-6 without however being completely respected since in this standard, the taken sample must be compacted by vibration or manually. Apart from the requirements concerning compaction, all the other recommendations of the standard NF EN 12350-6 can be applied including the data relating to the fidelity of its table 1. More simply, the method “c” described above for the dry process in the paragraph 2.5.1.1.1, can be used. 2.5.1.22.5.1.22.5.1.22.5.1.2 Measurement of consistencyMeasurement of consistencyMeasurement of consistencyMeasurement of consistency


With this technique, the measurements of consistency can be made only after projection and no method of compaction of a sample allows to reconstitute, in an Abrams cone for example, the consistency obtained by this projection. Very simple manual tests have always been practised by the experienced nozzlemen who test the penetration resistance with their thumb (or with a steel point Ø 2 to 4 mm) in the freshly sprayed concrete. This extremely qualitative and very useful test can advantageously be replaced by the measurement of the penetration resistance with a pocket penetrometer needle used by geotechnicians. The quantification of the test allows people without the experience of a qualified nozzleman to use it. Thus, it can be prescribed as a control test. It can be performed using a penetrometer measuring reactions going from 0 to 11 daN and whose conical point has an angle of 60 or 90° for a base Ø 8 mm.

Pocket penetrometer

As an indication, the following table gives an example of the information which can be obtained with a penetrometer measuring reactions from 0 to 11 daN and whose conical point has an angle of 60° and a base Ø 8 mm.



Measurements made during the 3 minutes following th e projection of a concrete without accelerating admixture

in daN (average of at least 3

measures)

Consistency

(for a concrete without accelerating admixture)

Water content in % of dry materials

< 0.5 very fluid Unfit for projection (except bottom slab) > 11 from 0.5 to 1 fluid Unfit for wall in very thick layer 10 ± 0,5 from 1 to 2 very plastic Unfit for vault and ceiling 9.5 ± 0,5 from 2 to 4 plastic Aptitude in all directions 9 ± 0,5 from 4 to 6 solid Good aptitude for vault and ceiling 8.5 ± 0,5 from 6 to 8 very solid Very good aptitude for vault and ceiling 8 ± 0,5 from 8 to 10 hard But risk of non-hydrated zones 7,5 ± 0,5

> 10 very hard High risk of non-hydrated zones < 7 In the case of a concrete with accelerating admixture, the measurement must be made during the 30 seconds following the projection. In the case of a concrete with setting and hardening agents (Guaranteed Initial Resistance (G.I.R.) concrete described in paragraph 2.5.4.1.1.) the measurement must be made with a different penetrometer (finer point and higher acceptable pressure strength). When the measurements of the penetrometric reactions are staggered, it becomes possible to record their evolution and to deduce from it the evolution of the sprayed concrete setting. For a concrete without accelerating admixture the measurements are taken, as far as possible, at 3, 5, 10, 15, 30, 60 minutes and for a concrete with accelerating admixture (except G.I.R.) at 1, 3, 5, 10, 15, 20 minutes, stopping as soon as the reaction 10 daN is reached.


No consistency measuring device especially adapted to projection by wet process is currently sold but some were developed by laboratories, sometimes by modifying materials designed for other uses. For example, for very fluid concretes sometimes used for projection with dense flow, a measurement of viscosity using a kind of “Marsh” cone with a very large nozzle (20 to 50 mm), possibly extended by an elbow, was successfully done. The V-funnel of the new standard NF EN 12350-9 is a variation of this cone with a very large nozzle. If this new standardized test gives satisfaction, it will formalise a very simple and effective test, with a material common to all. Another simple device measures the penetration resistance of a rubber pipe in a fluid plastic concrete (see 2.5.2.1.2.). Compared to the standardized slump test described in paragraph 2.1.2.2.1, the 2 measures previously given as examples have the advantage of giving information about the “pumpability” of the concrete which must be introduced into the pump and pushed in the pipe. In addition, they are quickly and easily done.



2.5.1.32.5.1.32.5.1.32.5.1.3 Measurement of the water content of the concrete in placeMeasurement of the water content of the concrete in placeMeasurement of the water content of the concrete in placeMeasurement of the water content of the concrete in place


We know that with this method, the loss by rebound of part of the aggregates (mainly the largest) causes an enrichment of the cement content. If this enrichment due to projection must be calculated, it is necessary to measure the water content of the concrete in place and this can be done only on site. This measurement is difficult because right after projection, the cement starts to be hydrated and this lowers the concrete water content. Thus it should be measured as soon and quickly as possible. The procedure has been used for more than 20 years on French building sites; it consists in drying the sample using methyl alcohol which is ignited. Then the burning mixture must be stirred constantly and the operation must be started again until constant weight.

Drying by alcohol: ignited sample stirred up constantly during its drying with a wooden handle spoon

Even if it is started very quickly after projection, this method takes several tens of minutes. The water captured by the cement during this time for its hydration is not free anymore and the water content (difference between the weight of the sample before and after drying) is lower than that which would be measured in a few seconds with a laboratory humidity meter.



It should be noted that this method cannot be used for sprayed concretes with accelerating admixture (all the more so GIR) or those containing quick-setting cement. Now, there are humidity meters that can be used on site. Asquapro plans to test their use on site for controls, as well as the exactness and the reliability of the measures. If these tests are conclusive, they could replace the drying by alcohol.


The cement enrichment being negligible in the wet process, its control is not of great interest; thus, the measurement of the water content (necessary for this control) is seldom prescribed. When the water content was prescribed, its measurement on site proved to be more difficult and less reliable than for the dry process because there was a greater quantity of water to be dried out by alcohol. In consequence and to our knowledge, the water content of freshly sprayed concrete by wet process is no longer prescribed. 2.5.1.42.5.1.42.5.1.42.5.1.4 UnderwaterUnderwaterUnderwaterUnderwater sieving of a samplesieving of a samplesieving of a samplesieving of a sample of of of of concretconcretconcretconcrete in place in place in place in place e e e


As for the two previous tests, the underwater sieving relates to projection by dry process of a concrete without accelerating admixture. It makes it possible to plot the mixture grading curve after its projection by adding to the curve of the non-passing on a 0.080 mm sieve the cement+ fine content of the produce going through this same sieve. The difference between the curves ordinates before and after projection represents the enrichment of the cement content + fine. We know the percentage of fine going through the sieve chosen for the test from the grading curves of the aggregates present in the mixture to be sprayed. It is then easy to deduce the cement content of the freshly sprayed concrete. If the water content has been measured, we can calculate the ratios W/(C+f) and W/C. But we should note that when the European standards on sprayed concrete testing methods were written, no requirement relating to the W/C was formulated; thus there is no standard requiring the calculation of this ratio. Nevertheless, the determination of the cement enrichment can be requested for some important and very technical building sites. Underwater sieving is then necessary.



Until now, the sieving was done on a sieve with a 0,080 mm mesh. This mesh size must be kept as the new sieves (0.063) are likely to prevent the passing of some cement particles. It would even be possible to use a sieve with a 0.100 or even 0.125 mesh provided that to deduct the percentage of sand and fine gravel elements going through these sieves for the calculation of W/C. The underwater sieving is a delicate operation when it is carried out on site. Thus, the engineers and technicians in charge of the external control must have been trained by specialists when it is recommended.


As it was written for the measurement of the water content in paragraph 2.5.1.3.2, the cement enrichment is negligible in the wet process. So its measurement is not necessary. Thus, the underwater sieving of a sample of concrete freshly spread by wet process does not need to be prescribed. 2.5.1.52.5.1.52.5.1.52.5.1.5 Sieve analysis of the Sieve analysis of the Sieve analysis of the Sieve analysis of the residueresidueresidueresidue on a 0.080 mm sieve on a 0.080 mm sieve on a 0.080 mm sieve on a 0.080 mm sieve This analysis can be made only when the underwater sieving described in paragraph 2.5.1.4 was carried out on site and that the residue was recovered from the 0.080 mm sieve. This residue being wet, a small part of the fine elements remains encrusted in the mesh. It is thus necessary to recover the sieve and its residue, cover it and put the whole thing in a tight bag. The first operation to be done at the laboratory is the oven-drying at 105° of the sieve and its residue. Then, after a traditional sieve analysis, the laboratory plots the curve representative of the residue and sends it to the person in charge for the external control who can then determine the grading curve of the concrete in situ after projection (see the example of March 13th, 1997 hereafter). This curve is obtained by adding to the residue curve of the laboratory, the residue found on site thanks to the underwater sieving and to the measurement of the water content. On the example, the increase of the cement content due to projection is the difference between the ordinates on the abscissa 0.080 (approximately 10%). Note that depending on the thickness of the sampling, on its position (wall, ceiling or sample box) and on the percentage of losses, the enrichment can reach 20 to 30%.



Example of grading curves before and after projection - realised in 1997

2.5.2 Tests on fresh concrete non-specific to sprayed concrete

2.5.2.12.5.2.12.5.2.12.5.2.1 Measurement of fresh concrete consistencyMeasurement of fresh concrete consistencyMeasurement of fresh concrete consistencyMeasurement of fresh concrete consistency Many non-standardized tests were developed to evaluate the consistency and various other properties of fresh concrete, poured in a formwork and then set up by manual compaction or vibration. For the dry process there are no tests non-standardized and non-specific to sprayed concrete concerning fresh concrete consistency. The tests specific to sprayed concrete were described in paragraph 2.5.1. For the wet process by diluted flow, there is no problem of pumpability so the tests on fresh concrete before projection are useless and those after projection having only a low interest are not used on site, as for the dry process. For the wet process by dense flow, the estimate of consistency is on the other hand very useful before projection to check that the concrete intended to be introduced into the pump is in conformity with the requirements and that it can be pumped and transported into the pipe to the nozzle, and then sprayed. The majority of non-standardized tests on fresh concrete, initially designed for poured concretes and usable for sprayed concrete with sometimes an adaptation of sampling, generally give relevant and reliable results, as long as of course they are carried out according to a precise procedure, defined by the equipment manufacturer or by a laboratory (for example, the LCPC for the workabilitymeter).

Curve of the dry S533 mixture

Curve of the in situ concrete after projection

MESH SIZE in mm

UNDERSIZE in %

SIEVE ANALYSIS OF CONCRETE SPRAYED March 13th, 1997



Given what was previously specified about the feasibility and the utility of tests on fresh concrete to control sprayed concretes, only those applicable to the wet process and really practised on French building sites are summarily described in the following paragraphs. They only relate to measurements of consistency and/or manoeuvrability.

2.5.2.1.1 Test using the plasticimeter with plates

This test is the first quoted because the device it uses is light, affordable and the measure is quickly done. For these reasons it is by far the most used on building sites, after the standardized slump test NF EN 12350-2. The device consists of a rod provided with plates at its lower end and a dynamometer with a rotating handle at its top. When the rod has been driven down into the concrete until the plates disappear in it, the handle is turned manually by a half-turn. This handle is linked to the rod by a system including the measurement device. The rotational movement of the handle is transmitted to the rod via a coil spring fitted to the rod by one of its ends and to the handle by the other end. The maximum deformation of the spring, which depends on the resistance encountered by the plates during their rotation in the concrete, can be measured and read directly on the handle thanks to an index. The link between the measured values and those of the slump test (NF EN 12350-2) being satisfactory for current concretes, the manufacturer of the device graduated the reading scale in centimetres of slump. The choice of this unit can be justified because a change of operator little affects the link and the concretes consistency expressed in centimetres of slump is the most commonly used in France. Nevertheless, it is questionable first because the plasticimeter measures a strength whereas the slump test measures a deformation but especially because the information given by the plasticimeter can be enough. For example this information could be translated into daN (considering the surface of the plates) or quite simply regarded as a shearing or viscosity index, without dimension. By applying this last proposal, the index measured in a few seconds estimates the suitability of concrete for being pumped and sprayed, as well if not better than the standardized slump test. The test can be frequently done, for example several times during the unloading of a concrete mixer truck. This allows, when the index reaches a value at which the person in charge for projection know there is a risk of blockage, to make a slump test and stop the provisioning of the pump if it is confirmed that the concrete is not in conformity anymore with the regulation concerning consistency.



In a nutshell, the plasticimeter with plates is very useful on building sites to frequently control the concrete pumpability and must be confirmed by a standardized test when it revealed that the limits of the prescribed consistency grade were likely to be exceeded and that there is a risk of litigation for nonconformity. It should however be noted that the plasticimeter with plates does not allow to measure an index for mortars or very fluid sand concretes which would have slumps higher than 20 cm.

2.5.2.1.2 Pompabilimeters

The aptitude of a concrete for being pumped and then introduced into a pipe of relatively low diameter in order to be sprayed is a property which it is very important to know before the pump is started to propel this concrete towards the nozzle. As it was indicated for measurements of consistency before projection by wet process, a small device to evaluate the pumpability in a few seconds using a simple pocket penetrometer provided with a hollow rubber end is even more practical and easy to use. It is called “pompabilimeter” in this guide, this neologism having the merit not to require a definition. With suitable ends it can test a traditional mixture as well as a very fluid sand concrete.

Pocket pompabilimeter



Evaluation of pumpability using a pocket “pompabilimeter”, before loading the pump

2.5.3 Tests on hardened concrete non-specific to sprayed concrete

2.5.32.5.32.5.32.5.3.1.1.1.1 NonNonNonNon----destructive tests on building sitedestructive tests on building sitedestructive tests on building sitedestructive tests on building site

2.5.3.1.1 Sonic echo-sounding with a hammer

2.5.3.1.1.1 General points

The testing by manual sounding with a hammer, whose realisation is often consistently recommended in many standards, aims to detect and locate the zones of sprayed concrete detached from their receiving surface. Unfortunately there is no testing method for this very common requirement. The hammer testing which is often recommended on the entire surface of a repaired or reinforced structure remains the most effective mean to detect the unbonded sprayed concrete plates that are likely to be detached. It is also useful to determine the zones apparently not detached although emitting a sound qualified as “hollow sound”. These zones can easily be delimited with a decametric precision but the characterization of the sounds located “with the ear” is subjective and badly defined.



To our knowledge no normative text gives any indication on how to qualify the sounds, to carry out the survey, to collect information, to record and exploit them. This is why the Asquapro guide presents hereafter a first attempt to fill this gap partially. May be studies were made on hammer testing , so we ask any person who would have knowledge of it to inform Asquapro so that this article of the booklet “Controls - part B” can take them into account. For this purpose, please contact:

[email protected] President of the technical committee

or

[email protected] Person in charge for the “Controls” technical guide

The texts which follow were based upon plausible assumptions which still have to be checked and perhaps to be modified. They thus constitute only the first approach of future studies for which research is to be undertaken. The reports concerning hammer testings written by persons in charge for external controls would be very useful to feed these studies.

2.5.3.1.1.2 Qualification of the sounds

Manual hammer testing allows to distinguish the zones where the strike emits a sound apparently without resonance generally qualified as “full” or “dull” sound, and other zones where sounds less short and more or less deep, qualified as “hollow” sounds, indicate that the struck surface right on the point of impact clearly vibrates. From 2002 to 2004, it was noticed that on approximately 6000 m² of sprayed concrete intrados coating implemented in a tunnel, the “hollow sounds” created by the strike of a hammer on the sprayed coating had different intensities, frequencies and sounds. These differences come from the surface and the thickness of the spread concrete zone under vibration and from the volume of the sounding board. This sounding board does not exist between the sprayed concrete and its support (which can be made of concrete, masonry, wood, steel plate, etc), if the adhesion is perfect. However, it is however to get a “hollow” sound when the adhesion between the concrete and the support is perfect but it is the support itself which creates the sounding board. In this case it can come for example from a masonry whose infill is still sufficiently compact so that it can vibrate if a sounding board is formed at the back (for example because of a vacuum in the surrounding ground in a tunnel). The first difficulty for the writing of a hammer testing report comes from the fact that the qualifying terms “full” and “hollow” should not apply to sounds.



For the “full” sound it would be wiser to call it “dull” but it does not really matter as these impact sounds are easy to identify. Whatever their name, they generally concern more than 95% of the examined surface. The problem is more complicated with the zones emitting “hollow” sounds because there are several kinds of hollow sounds. Some are very frequent when the vibrating surface is small; for some others, the larger the vibrating surface is (more than 1m² sometimes), the deeper they are (lower frequencies). In the absence of more adequate words yet to be defined, to tell the difference between them in the reports the expressions “weak hollow sound” and “hollow sound” have been used until now. The CETU (tunnels study centre) who carries out many hammer testings to examine the structures for which it must make the diagnosis, uses “hollow sound" and “cavernous sound” which is clearer but it comes down to the same thing. With these two categories of hollow sounds, it was possible to trace on the plans of the examined surfaces the outlines of these two types of “resonating” zones which were filled by slightly different colours. It is possible that the planned studies will allow to better distinguish the sounds and that three or four categories may be defined.

2.5.3.1.1.3 Manual hammer testing procedure

Manual hammer testing must help distinguish the zones where the stroke emits a “full” or “dull” sound, and other zones where sounds, less short and more or less deep, qualified as “hollow” sounds, indicate that right on the point of impact, the struck zone vibrates. To carry out manual hammer testing the sprayed concrete must be set, which is generally the case after 24 hours by dry process, with even mixtures without accelerating admixtures, when the temperature is higher than 10 degrees. By wet process, in cold weather and when a slow cement is used (CEM 3 C 42.5 for example) it is necessary to wait 48 hours or even more with a concrete with an accelerating admixture. Considering the differences of the setting times previously indicated, hammer testing can thus start the following day for the dry process (except in very cold weather) and two days later or even more for the wet process. As this hammer testing is very important to detect low adhesion surfaces it must be done daily. In consequence, it must be done under the internal audit by the technicians of the company who were designated as responsible for this control. The procedure described below must thus have been proposed to the project manager in the Quality Assurance Plan of the company.



Example of procedure: To seek the “hollow” sounding zones, the person in charge for the internal audit must strike with a hammer all the facings sprayed 24 or 48 hours before (or more if necessary, see above). For this systematic test the strokes must be spaced every 20 to 40 cm all over the surface. When a hollow sound is detected, the zone must be bounded by striking around, approximately every 10 cm. The suspect zone must then be marked on its entire circumference directly on the structure using an indelible spray paint or a marker, and then numbered. Comparative tests were carried out with the CETU by using two different hammers. It appeared that the use of a geologist hammer with a steel handle is not necessary (it is too heavy - 850 grams - for the operator when there are large surfaces to probe). A small hammer weighing from 300 to 500 grams with a wooden handle securely attached detects the suspect zones with as much precision. Hammer testing can be repeated after several weeks or months as long as the zones located on the structure are visible and accessible. The marking on site is copied on the plan or on a part of the developed plan of the structure (see example on the following page).

List of the hollow sounding zones

The hollow sound is produced when a more or less extended zone of the facing vibrates when it is hammer tested. Speaking of the stroke, the sound depends on the type of hammer, on the energy of the shock and on the hardness of the facing on the point of impact whereas speaking of the struck surface, the sound depends on the surface and thickness of the slab vibrating as well as on the volume of the sounding board. Without devices to measure (or better: to record) its characteristics, the sound can be estimated only qualitatively “with the ear” depending on its pitch, its intensity and its timbre. This qualitative estimation is nevertheless useful so that the examination of the list of the suspect zones on the developed plan of the structure allows to place some of these zones under supervision. A test campaign made 5 years later measure the evolution of the suspect surfaces, even if the marks on the structure are canceled.



Section (approx. 10% that is to say 600 m²) of a measure

carried out in 2004 with its key

Plan of 2 types of “hollow” sounds on a tunnel surface of 600 m²

The zone with a real “hollow” sound is located at PM 250 at 2 hours and measures approx. 3 m²

2.5.3.1.2 Measurements of sclerometric indices

These measurements which can be made 24 or 48 hours after concrete projection give information on its short-term quality. The objective of the measurements referring to external control on a sprayed concrete building site is to know as soon as possible if the quality of the sprayed concrete is acceptable or not without awaiting the results of the tests at 7 or 28 days on core specimens. It uses a sclerometer identical to the one used to determine the rebound index described in standard NF EN 12504-2 (see paragraph 2.4.2.4). It was thus decided to ask the persons in charge for external control for fewer impacts than the number recommended in the standard in order to increase the number of tested zones.

LEFT BANK

RIGHT BANK

KEY

UPSTREAM

KEYS

Weak « hollow » sound

« Hollow » sound

Wetland

Thin crack

Water inflows

PVC weephole

Convergence plot

Sclerometer test range



2.5.3.1.22.5.3.1.22.5.3.1.22.5.3.1.2.1.1.1.1 ProcedProcedProcedProcedure:ure:ure:ure:

Except for the number of impacts per zone which is different, all the other requirements of the standard NF EN 12504-2 must be respected and the tested surface quality (roughness, moisture) and the stroke orientation noted. Depending on the chosen tested zone, this orientation of the sclerometer can be horizontal for the impacts on vertical walls (or side walls for tunnels), vertical downwards on floor (or in the axis of the apron for the tunnels), vertical upwards under ceiling (or keystone for tunnels), at 45° upwards or also 45° downwards. The controller must make at least 9 impacts per tested zone (3 lines of 3 for example) and calculate the median value of the measurements. The tested zones can be: � on the facing of a final layer levelled with a ruler or floated, then sandpapered on a

surface of approximately 400 cm² after the concrete has hardened � when the concrete is rough, on a zone summarily drawn up after projection on

approximately 400 cm², sandpapered thanks to a grinding machine or using the abrasive stone of the sclerometer, after hardening of the concrete.

The recorded median values as well as the date of projection are noted on each zone of the structure with an indelible marker. These indications will ease the next measurements a week or a month later, in order to follow the evolution of the strengths and to possibly compare them with those obtained on the test specimens.



2.5.3.1.2.2. Location of the measurement zones

The location is done directly on the structure by circling each tested zone with an indelible marker then by numbering it and by indicating the projection date. Depending on the place of the located zone, the inclination of the sclerometer can be deduced since the stroke must be perpendicular to the wall. These measurements must be made 1 or 2 days after projection, and then possibly at 7 days, 14 days and 28 days (if it is possible), on sandpapered and located surfaces. It is essential to indicate the measures on the developed plans of the structure: this will ease other measurements in the longer term and will help to make them at the right place even if markings have disappeared.

Material:

� Sclerometer. The type must be indicated (for example: Schmidt type N) � Grinder or abrasive stone � Indelible marker

2.5.4 Tests on hardened concrete specific to sprayed concrete

2222.5.4.5.4.5.4.5.4.1.1.1.1 Strength at young agesStrength at young agesStrength at young agesStrength at young ages Since sprayed concrete has been used for underground works a sufficient concrete resistance is always sought to obtain a support within the shortest possible time. Unfortunately, drilling out a sample is almost impossible as long as the compressive strength of the concrete does not exceed 1 MPa because aggregates come off and turn with the diamond corer. Various methods were thus imagined to solve this problem in order to estimate the resistance of a young sprayed concrete, apart from those developed in Austria for underground works (used in standard NF EN 14488-2 and described in this booklet in paragraph 2.3.2). The following procedure, developed by the SNCF, is used.

2.5.4.1.1 "G.I.R” Procedure (Guaranteed Initial Res istance)

For a reason different from that of the fast creation of a support, the SNCF asked the companies to spray - for works in tunnels which are in operation - a concrete having quickly a strength high enough so that the circulation of the trains can be restored approximately 3 hours after its projection.



The G.I.R. procedure is used to qualify dry basic mixtures, manufactured in plants and allowing to obtain at the temperature of 10° a resistance ≥ 3 MPa after 3 hours. Therefore, for the tests at 3, 5 and 24 hours, the coring is replaced by the sawing of 10 cm x 10 cm cubes out of sprayed slabs. The test-tubes intended for longer-term tests (at 7, 28 and possibly 90 days) will be cored out instead of sawn out. When control tests at 3 hours are required, it is essential to have on the building site a mobile laboratory equipped with a large diameter diamond saw to cut out the 10x10x10 cm cubes and with a press to crush them. In this case, the company must then spray the samples in 50x50x15 or 60x60x15cm boxes from which the cubes will be sawn out. The projection must be carried out with the personnel, material and equipment envisaged for the works (in the case of suitability tests) or with those used on the building site (in the case of control tests). The nozzleman must regulate the supply of water at the nozzle to obtain the desired consistency before spraying in the box. He must then start with the edges and do his utmost not to trap losses in the slab. The indications for the installation of the box at less than 20 degrees of the vertical plane as for the standard NF EN 14888-1 apply. To be on the SNCF list of suitable candidates, and for on-site controls, the results to obtain are as follows: at 3 hours: ≥ 3 MPa if the temperature is 10°c ≥ 1.5 MPa if t=2°C at 24 hours: ≥ 10 MPa and at 28 days: ≥ 25 MPa



3 FREQUENCIES OF THE TESTS AND MEASUREMENTS

The minimum frequencies are defined in table 12 of standard NF EN 14487-1. In this table, reference is made to “categories” which relate to the inspection levels and which must have been defined by the project manager in his call for tender. On site, the personnel only have to respect the frequencies prescribed in the table 12 of the standard, according to the inspection category indicated in the contract. For the managers of the company in charge for the internal audit and for those of the design office and the laboratory in charge of external control, we recall below some information which is better detailed in the booklet “Controls” – Part A, paragraph 3. Readers may thus refer to it.

3.13.13.13.1 INSPECTION CATEGORIESINSPECTION CATEGORIESINSPECTION CATEGORIESINSPECTION CATEGORIES

There are 3 categories of inspection level: • Category 1: it relates to works requiring only a low inspection level • Category 2: it relates to works requiring a medium inspection level • Category 3: it relates to works requiring the highest inspection level Examples which have helped the project manager to determine the inspection category for the work depending on its risk level, are given in appendix A (informative) of standard NF EN 14487-1. These categories take account of the risks incurred by the works (stability, longevity), by their users and their residents and by their environment (nearby structures, dwellings, etc).

3.23.23.23.2 Table of minimal frequenciesTable of minimal frequenciesTable of minimal frequenciesTable of minimal frequencies

These frequencies are defined in the table 12 of standard NF EN 14487-1 according to the inspection category which was chosen by the project manager and to the type of work. Please refer to this table.

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