EFFECTS OF ACIDITY PRESENT IN WATER ON STRENGTH AND SETTING PROPERTIES OF CONCRETE

H. Sudarsana Rao*, J.N.T. University, India

V. Venkateswara Reddy, J.N.T. University, India S.G. Vaishali, J.N.T. University, India

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29th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 - 26 August 2004, Singapore

EFFECTS OF ACIDITY PRESENT IN WATER ON STRENGTH AND SETTING PROPERTIES OF CONCRETE

H. Sudarsana Rao·, J .N.T. University, India V. Venkateswara Reddy, J.N.T. University, India

S.G. Vaishali, J .N.T . University, India

Abstract

This paper deals with the effect of hydrochloric acid (Hel) and sulfLiric acid (H2S04) present in mixing water on properties of setting times, compressive strength and tensile strength of cement concrete. The results indicate that the initial and final setting times get retarded due to acidity imparted by Hel and H2S04. HydrochloriC acid when present in water retarded the initial and final setting times considerably when its content was exceeded by 500 mg/L and 300 mg/L respectively. Sulfuric acid retarded the initial and final setting times significantly when its content exceeds 300 mg/L in mixing water. The rate of development of compressive strength and tensile strength decreased with the increase in concentration of both Hel and H2S04 for 28days and 90 days. However this decrease is significant at concentration of 500 mg/L and 300 mg/L for Hel and H2S04 respectively.

Keywords: cement concrete, setting time, compressive strength, tensile strength, acidity

1. Introduction Concrete is one of the most widely used construction materials, because of its good durability to cost ratio. However, when subjected to severe environments its durability can significantly decline due to degradation of concrete. Cement using in concrete is a mixture of complex compounds. The reaction of these with water leads to setting and hardening of cement when it is gauged with water. The C~ (Tricalcium aluminate), C3S (Tri calcium silicate) and C,.AF (Tetra calcium alumina ferrite) phases react very rapidly and the gauging water become saturated with Ca(OHh formed in the hydrates rather slowly. The initial setting is attributed to hydration reactions. The C2S (Dicalcium Silicate) phase the reactions of C3 A, C3 S and C,.AF (lea, 1956). The aqueous phase is essentially a solution of the hydroxide and sulphates of Ca, Na & K and it is likely that equilibrium sets in among then (Price, 1951).

The quality of the water plays an important role in the preparation of concrete. Impurities in water may interface with the setting of the cement and may adversely affect the strength of the concrete (Neville, 1970). The chemical constituents present in water may participate in the chemical reactions and thus affect the setting, hardening and strength development of concrete. A popular yard stick to the suitability of water for making concrete is that if it is fit for drinking, it is fit for making concrete. The IS 456 (2000) code stipulates the water quality standards for mixing and curing of concrete works. In some arid areas, local drinking water is impure and may contain an excessive amount of acids due to contamination by industrial wastes. The effects of acids on setting, hardening and strength development of cement concrete are not known much. Hence, an investigation is carried out in order to evaluate the effect of acids (hydrochloric acid & sulfuric acid) in setting time and strength of concrete under laboratory conditions. The results of the same are presented in this paper.

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2. Materials and Methods

Cement: The cement used in the present investigation is of 53 grade ordinary Portland cement. The percent composition of the major compounds present in cement are presented in Table-1

TABLE: 1 Percentage compositions of the major compounds present in the test cement

SloNo Name of the compound

Conversion fonnula % Present in Cement

1 Tricalcium silicate (3CaO Si02)

4.07(CaO)-7.6(Si02>­6.72(AI203)-1.43(F~03)-2.85(S03)

51.49

2 Dicalcium silicate (2CaO Si021

2.87(Si02)-0.754(3Cao Si02) 23.37

3 Tricalcium aluminate (3CaO Alz0 2)

2.65(Alz0 3)-1.69(Fez0 3) 9.31

4 Tetracalcium alumino ferrite (4CaO AI20 2 Fe203)

3.04(Fe20 3) 11.70

Fine Aggregate: The fine aggregate used in this investigation is the river sand obtained from Pandameru River near Anantapur in Andhra Pradesh. The properties of sand are presented in Table -2.

Table: 2 P roperties 0 f sand Slo Property Unit Result NO 1 Specific Gravity 2.75 2

-Bulk Density KNlm"' 15.54

3 -Fineness Modulus 2.80 4 Particle size variation Mm 0.09 ­

2.0 5 % 0.124

concentrated Hydrochloric acid

Loss of weight with

Coarse aggregate: Crushed Granite stone aggregate of maximum size 20 mm confirming to IS 383-1970 was used. The specific gravity and fineness modulus were found to be 2.622 and 6.65 respectively. Test results are shown in Table 3.

TABLE: 3 Grading analysis for coarse Aggregate Sample-5000 gms

SLNO 1.5. Sieve size

Weight Retained (gms)

Cumulative weight retained (gms)

Cumulative Dk retained

% passing

1 80mm - - - 100.00 2 40mm - - - 100.00 3 20mm 830.00 830.00 16.60 83.40 4 10mm 1190.00 2020.00 40.40 59.60 5 6.30mm 310.00 2330.00 46.60 38.60 6 4.75mm 740.00 3070.00 61.40 53.40 7 2.36 mm 1930.00 5000.00 100.00 -8 1.18 mm - - 100.00 -9 600 microns - - 100.00 -10 300 microns - - 100.00 -11 150 microns - - 100.00 -

Total 5000.00 665.00

Fineness Modulus=665.00/100 = 6.65

510

Water: Deionised water spiked with hydrochloric acid and sulfuric acid at different concentration is used in mixing water.

3. Experimental System The following equipment is used for casting and testing of the specimens.

i. Cube and cylinder moulds. ii. 40T U.T.M (Universal Testing Machine) for cube compressive strength determination. iii . Vicat's apparatus including moulds confirming to IS 4031 (part 5)-1988. iv. Cement concrete cubes and cylinders of M20 and M50 grade are casted with water

containing , hydrochloric acid and sulfuric acid in the concentration of 100, 150, 300, 500 and 900 mglL in mixing water.

Setting Time Vicat's apparatus confirming I.S. 4031 (pant 5) 1988 consists of a frame to which a movable rod having an indicator is attached which gives the penetration, weighing 100gms and having diameter and length of 10 mm and 50 mm respectively. Vicats's apparatus included three attachments­square needle for initial setting time, plunger for determining normal consistency and needle with annular collar for final setting time

Compressive Strength The test specimens for the determination of compressive strength of concrete are prepared using the standard metallic cube moulds adopting I.S procedure for the rodding and hard compactions.

The cubes are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix the cubes are tested for a compressive strength after 28 days and 90 days. The compressive strength is computed as the average value of the three samples .

Split Tensile Strength The test specimens for the determination of split tensile strength of concrete are prepared using the standards metallic cylinder moulds adopting I.S procedure for the rodding and hard compaction. The cylinders are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix. The cylinders are tested for split tensile strength test after 28 days and 90 days. The split tensile strength is computed as the average value of the three samples.

4. Results and Discussion The interpretation of results obtained in this investigation is based on the guidelines specified by IS 456 (2000) .

The average of both the setting times of three cement samples prepared from water under consideration are compared with those of the cement specimens prepared from deionised water. If the difference is less than 30 minutes, the change is considered to be negligible and if the difference is more than 30 minutes, the change is considered to be significant.

Average compressive strength and average split tensile strength of at least three specimens prepared with water under consideration is compared with that of three similar cases prepared with deionised water (Control) . If the difference in the strength is less than 10% it is considered to be insignificant.

Setting Time Test results of setting times of the test block made from different water samples and deionised water are reported in fig. (1) & (2).

From the fig 1 & 2, it is observed that both setting times are increased with the increase in concentration of hydrochloric acid and sulfuric acid of mixing water. Considerable increase in both the initial and final setting times is observed when amount of hydrochloric acid was 500 mg/L and 300 mglL and this significant change observed at 300 mglL of sulfuric acid in mixing water for both initial and final setting times .

511

-----

400

1000

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. '''''H'

/ (FIMI)

~-e- - Fine!

;- .......~...-'""n / (tnitJ.II)

450

.., .400

.. J60 ~ 350 co <=]300 EJOO E21>O

i: S 250

.Ii II

.~ 2DO

g' .10 :; ~100

00f':l , , , , ·9 "-"9 AllCl .@ - "llllP

CoooeAIralion CI ~CI.;n ~L

... perm ,.."mfm'ill'· '" (Final)

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• ,......." .'V . " .. (Initdll)

I

Fig. 1.variation of Setting times of cement corresponding to various concentrations of HC) in deionised water

~~-----------------------------, -400

;350 1:300 E ,52:10I_ :r11O

!100

50

0 200 _ 100 eoo

) ..... " ..._"',.." (Final)

,

~o FNI

~ ' .....

(Initial)

o control Concentratiof1 of H2SO4 In gIL

Fig. 2.Variation of Setting times of cement corresponding to various concentrations of H2S0~ in deionised water

Compressive Strength Test results of the cubes prepared from water containing different salts are presented in fig. 3.

As indicated in fig.3 the compressive strength of the specimens decrease with increase in concentration of hydrochloric acid and sulfuric acid of mixing water. But the increase in compressive strength was considerable when the concentration hydrochloric acid was 500 mglL in mixing water and this Significant change observed at 300 .mglL of sulfuric acid in mixing water for both 28 days and 90 days strength.

·...-_·21 _ __4- IIZO~ _.,.

• · 1150.-,0 -1'- IlJO.HMyo

_ ~ I'19JJ _ m _ _ _

·~(Jft:\CI"'9i .co.oga,.~'d~;in¢

(a) (b) Fig. 3.Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) HCI (b) H2S04 in deionised water

512

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig . 4.

From fig.4 it is observed that the split tensile strength of the specimens decreases with increase in concentration of both hydrochloric acid and sulfuric acid of mixing water. But the increase in tensile strength was significant when the concentration hydrochloric acid was 500 mglL in mixing water and this significant change observed at 300 mglL of sulfuric acid in mixing water for both 28 days and 90 days strength.

~

,2

i ...i ... 1 ... 1"0 -' . 12

t·,.fi ...e # .,"

, 2<)

''l ­...'" ......... -"" ,

"-. "

f ·

.0 2IlSl ~ ~

~i9n~!1ICI;n¢

(a)

~~_ZJ Myo

- <>- .,-..".. .,60·ZJayo ---.-. .,60..0..."

~-----. "?

eQ(l

0 "

~-';:...

"t ....f..1" 0 -' ·'6 '-..

t£ .20 .,. ·26 -~QQ!) ~ '2!lO «>0

__ r.t2B-2.e cloys

- .• ~- JoI2O-4IO cloys . ~2.edIys

-~

'e

!Ill!> = .(4)IIMUlII:IIIicIn &II H2S04I ,., ¢

(b) Fig. 4.Percentage Variation of tensile strength of concrete corresponding to

various concentrations of (a) HCI (b) H2S04 in deionised water

5. Conclusions

Based on the present investigation, the following conclusions can be drawn: a. Hydrochloric acid and sulfuric acid when present in mixing water retards both the initial and

final setting times. b. Hydrochloric acid retards the initial and final setting times significantly at concentrations of

500 mglL and 300 mg/L respectively. c. Sulfuric acid retards the initial and final setting times significantly at concentrations of 300

mglL. d. Hydrochloric acid and sulfuric acid when present in mixing water decreases the

development of compressive and tensile strength. e. Hydrochloric acid decreases the compressive and tensile strength significantly at

concentrations of 500 mglL. f. Sulfuric acid decreases the compressive and tensile strength significantly at concentrations

of 300 mglL

6. References

i. IS 456:2000: Code of Practice for Plain and Reinforced Concrete. ii. IS 383; 1970: Specification of Coarse and Fine Aggregates from Natural Sources fQ{

Concrete (Second revision) . iii. IS 4031 968: Methods a Physical Tests for Hydraulic Cement iv. Lea, F.M. (1956) : The Chemistry of Cement and Concrete, Edward Arnold (Publ.) Ltd. v. Neville AM. (1970): Properties of Concrete, The English Language Book Society, Pitaru

Publishers. vi. Price, W.H.(1951): Factors influencing concrete strength, A. C.I. , Vol. 47 , pp 417

513