TR/AR/061

Haji Hassan Readymix

Technical Report

(Addendum to TR/AR/054)

Temperature Monitoring Report For

Mohammed Jalal Contracting,

Mass Concrete PourR50 Rectifier Foundation, ALBA

June 2014

Minimum Pour Dimension, m

Introduction

In January 2014 Haji Hassan Readymix submitted Technical Report TR/AR/054 which provided guidance to control the temperature of in situ concrete of a 1.5m deep slab for the R50 Rectifier at Alba, Bahrain.The Client (ALBA Aluminium), the Consultant Engineers (Ismail Khonji & Associates) and the Contractor (Mohammed Jalal Construction) duly took note and agreed the following.

The approved mix design was HHRM mix reference 28138-F3 (full details given in Appendix A) using 30% Pulverised Fly Ash and having an expected performance as shown in the laboratory trials (see Appendix B). The design margin of 4.2N/mm2 was lower than normal. However, the strength gain of PFA mixes up to 56 Days provided a comfortable degree of safety and avoided having to increase cement; this would have exacerbated the in situ temperature problem.

The expected temperature rise was estimated from the graph below taken from BRE Digest 3 “Mass Concrete”. Using 30% PFA at 400kg/m3 for pour depth 1.5m there was an expected temperature rise of 35°C.

When added to fresh concrete temperature of 32°C a peak of 67°C was derived. This is below the theoretical maximum of 70°C which in turn provides the margin for a practical in situ maximum of 75°C.

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It was noted that the potential problem with high in situ temperatures, Delayed Ettringite Formation (DEF) was significantly reduced by fully tanking the structure (DEF requires an external source of water to proceed).

The target maximum temperature differential within the pour was 30°C. This is below the theoretical maximum of 38°C (for limestone aggregate concrete) and provides a comfortable margin.

The agreed monitoring procedure was to be carried out by Qatar Engineering Laboratories using thermocouples (Ref TH1 – TH6) at locations designated by HHRM. The locations were selected to pick up the peak temperatures and maximum temperature differentials as shown below

Diagram 1: Thermocouple Locations

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The data analysis is from 230m3 concrete ordered on 22nd May 2014 starting at 0700hrs with fresh temperature 29.0°C at site and ambient temperature 32°C. The pour was completed at approximately 1400hrs using 217m3 of concrete with fresh temperature 31.5°C at site; ambient temperature reached 38°C by the time of pour finishing.

This report contains the data from the concrete pour and from QEL’s monitoring. It compares the theoretical values with those actually achieved and makes relevant comments regarding any deviations from expected behaviour.

Executive Summary

Internal concrete temperatures peaked at 70.3°C (TH1) and 70.0°C (TH5). This was higher than predicted by 3°C but remains below the signal value. The solar gain due to lack of shading or fogging will have contributed to this.

The maximum differential was 27.6°C between TH5 and TH6 occurring 70½ hrs after pouring was completed. This is below the signal value.

Concrete strengths are in line with trial mix data at 7 days (28 day results due on 19th June 2014) and summarised below. C45 compliance is predicted.

Test Type Test Reference

Date Compressive Strength, N/mm27 Days 28 Days

Lab trial LT12 28/1/14 35.8 49.2Field Test 1615 22/5/14 36.0

Due 19/6/14Field Test 1616 22/5/14 37.8Field Test 1617 22/5/14 34.8Field Test 1620 22/5/14 35.9

No problems relating to pour timings and supply rates were reported.

Temperature Monitoring

QEL’s data from thermocouple readings are given in their report #12071 (see Appendix C).

Appendix D contains more in depth analysis and full-size versions of the graphs used in the following discussion.

Discussion of results

Data shows the following.

1. Peak temperature is 70.3°C (see Graph 1)

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Graph 1: Thermocouple Readings

Centre (1)

Centre (5)

Top Centre (2)

Entrant Corner (3)

External Corner (4)

External Corner (6)

Ambient

Time Elapsed, Hours

In S

itu

Tem

pera

tutr

es, C

entig

rade

2. By the time concrete pour reached half depth at 750mm (up to TH1) ambient temperature had reached 34.3°C

3. Each thermocouple was immersed in turn by concrete as follows (See graph 2)

TH1 at 1100hrs, ambient at 34.3°C TH5. at 1120hrs, ambient at 35.5°C TH2, TH3 & TH4 at 1200hrs TH6 at 1330hrs

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.029.0

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Graph 2: Early Thermocouple Readings

AmbientExternal Corner (4)Top Centre (2)External Corner (6)Centre (5)Centre (1)Entrant Corner (3)

Time Elapsed, Hours

In S

itu T

empe

ratu

tres

, Cen

tigra

de

4. All deliveries showed temperature increase in situ from solar gain & ambient temperature of approximately 0.3°C/hr (Graph 2). This will increase the peak temperature.

5. Thermocouple readings were affected by ambient temperature as shown in Graph 3 overleaf

8 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80 830

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26Graph 3: Difference between ambient and in situ concrete

Mid-dle - Am-bientTop Mid-dle - Am-bientEn-trant Corner (3) - Ambi-ent

Time Elapsed, Hours

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ture

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tial,

Centi

grad

e

8 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80 832022242628303234363840424446

Ambient Temperature

Time Elapsed, Hours

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ture

, Cen

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There is a time lag of 3 to 4 hours between ambient temperature trends and the response from in situ (at 100mm depth)

Overnight cooling rates increased with distance from the centre of the pour; the temperature drops of TH3, TH4 & TH6 exceeded that of ambient (due to their higher starting temperature) resulting in a reduction in the difference between them.

TH2 showed a cooling rate equal to the ambient cooling rate indicating that the production of heat from within was enough to offset the heat loss at the surface.

The core temperature was unaffected by ambient conditions

Conclusions

Changes to the original concrete specification allowed the pour temperature to be controlled within acceptable parameters and may be considered a success.

The structure has a characteristic strength of C45 and meets the durability requirements given in BS8500-2 for DC-3 exposure conditions for 100 year design life.This includes sulfate exposure to DS-4 as shown in Table A2 from BS8500-1 (see below) and with 75mm cover meets the requirements for 100 year design life with respect to non-marine chloride exposure and carbonation

Author Details

Andy Rogers holds the Diploma in Advanced Concrete Technology with over ten years experience as Technical Manager with RMC (now Cemex), two years with Readymix Qatar and two years spent in Libya as Concrete and Materials Consultant for the Great Man Made River Project. He is currently the Technical Manager for Haji Hassan Readymix

This report is, to the best of my knowledge, factually correct.

Signed Date

Appendix A

Mix Design

. Appendix B

Laboratory Trial Data

Appendix C

Qatar Engineering Laboratory Temperature Monitoring Report

Appendix D

Graphical Analysis of Temperature Recordings