The Intemational Joumal of Cement Composites and Lightweight Concrete, Volume 5, Number2 May 1983

Technical notes: Influence of polymer microparticles on acid resistance of structural lightweight aggregate c o n c r e t e Satish Chandra • and Leif Bemtssonf

*S. Chandra is research assistant at the Division of Building Materials, Chalmers University of Technology, Sweden. His research work includes study of reaction mechanism and chemical durability of lightweight aggregate concrete, high strength concrete and polymer concrete. fL. Bemtsson is research associate at the Division of Building Materials, Chalmers University of Technology. His main research works are within lightweight aggregate concrete, high strength concrete, polymer impregnated concrete, vibration and accelerated curing.

© Construction Press 1983

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SYNOPSIS The influence of film-forming polymer microparticles on the acid resistance of structural lightweight aggregate concrete is studied. These results are compared to those of structural lightweight aggregate concrete made with conventional air entrainment (CAEA). The effect of film-forming microparticles addition is also studied on normal concrete. It is concluded that the film-forming microparticles used increased the resistance to hydro- chloric and lactic acids of the structural lightweight aggregate concrete as well as of normal concrete.

KEYWORDS Lightweight concretes, structural engineering, concrete durability, acid resistance, chemical tests, hydrochloric acid, lactic acid, sulfuric acid, liquid polymers, crosslink- ing, air entrainment, aggregates, weight loss, deteriora- tion, cracking (fracturing).

INTRODUCTION A special type of structural lightweight concrete (3L-concrete) has been developed at Chalmers Univer- sity of Technology using expanded clay aggregate and special optimized polymer dispersion (Cemos). Cemos is a styrene-methylmethacrylate dispersion and contains soft microparticles of 0.1 /~m diameter. The particles have film-forming ability (M FT < 30°C), and considerably improve the freeze-thaw durability of structural light- weight aggregate concrete [1 ]. In this study the effect of these microparticles on the acid resistance of light- weight aggregate concrete under laboratory conditions is reported. Comparison of test data is made with lightweight aggregate concrete containing conventional air entraining agent. The effect of microparticles is also studied on normal concrete. The acids used for tests are hydrochloric acid (HCI), sulfuric acid (H2SO,) and lactic acid (CH~.CHOH.COOH). Further the resistance of cut sections as well as uncut sections of lightweight aggregate concrete and normal concrete is tested.

MATERIALS AND TEST METHOD Lightweight aggregate concrete prisms (6 x 6 x 12 cm) were made with film-forming polymer dispersion (Cemos) and expanded clay aggregate. Prisms were also made with conventional air entraining agent. For comparison purposes specimens of normal concrete were made with and without Cemos. The concrete composition, and some physical and mechanical properties are shown in Table 1. The specimens were stored for 28 days in a climate room at about 50% RH and 20°C. Later they were stored in water for 28 days. The compressive strengths shown in the table were measured after 28 days storage in climate room. Cut surface specimens were made by cutting 6 x 6 x 12 cm prisms from bigger pieces so as to have one side (6 x 12 cm) sawn.

Solutions of 15% hydrochloric acid, 5% sulfuric acid and 5% lactic acid were made. The concentrations of hydrochloric acid and sulfuric acid were chosen on the basis of the previous work done at Brookhaven National Laboratory [2]. The concentration of lactic acid was

127

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Influence of polymer microparticles on acid resistance of structural lightweight aggregate concrete Chandra and Bemtsson

chosen similar to sulfuric acid. The specimens were continuously immersed in these solutions and weight changes were noted at regular intervals. The test method followed for hydrochloric and sulfuric acids is the same as that used by de Puy [3]. In all cases the concentration of the acid solutions was kept constant by titrating them against alkali solutions using methyl red as indicator. The results are presented in graphical form in Figures la, l b and lc. One of the typical examples of

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Figure 1

C

N

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Type o f conc re te

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Percent weight loss for concrete after storing in a) 15% hydrochloric acid solution for 3 months b) 5% sulfuric acid solution for 6 weeks c) 5% lactic acid solution for 3 months

N - Normal concrete NA - Normal concrete with Cemos

L - 3L-concrete (Lightweight aggregate concrete with Cemos)

LB - Lightweight aggregate concrete with conventional air entraining agent

C - Cut sections Size of the specimens 6 x 6 x 12 cm

damaged specimens by hydrochloric acid is shown in Figures 2a and 2b.

b)

i ̧

Figure 2 Corroded specimens after storing in 15% hydrochloric acid solution for 3 months. a) uncut specimens b) cut sections

LB - Lightweight aggregate concrete with conventional air entraining agent

L - 3L-concrete NA - Normal concrete with polymer

microparticles (Cemos) N5 - Normal concrete Size of specimens 6 x 6 x 12 cm

RESULTS AND DISCUSSIONS

Hydrochloric acid attack The results of concrete deterioration in percent weight loss are shown in Figure l a and the physical appearance of the specimens in Figure 2a for uncut concrete specimens and in Figure 2b for cut specimens. During the test it was observed that the outer surface of the specimen was yellow whereas the inner was brown. This is caused by the difference in Fe(OH)3-content as confirmed by Rubetskaya et al [4]. It is evident from the results obtained that the minimum

129

Influence of polymer microparticles on acid resistance of structural lightweight aggregate concrete Chandra and Berntsson

damage occurred in the lightweight aggregate concrete with microparticles (3L-concrete) and maximum in the normal concrete. Further the difference is more pronounced in the normal concrete without polymer microparticles.

3L concrete is less damaged than the lightweight aggregate concrete with conventional air entraining agent. The reason for this is attributed firstly to the change in the structure of the concrete because of the addition of microparticles as explained elsewhere, providing a more compact structure, and secondly to the hydrophobic character that the microparticles have imparted to the concrete reducing the absorption property [5]. Due to this the penetration of the acid was slower than without microparticles. A third reason is the complex formed due to the reaction between calcium hydroxide and carboxytate ions of the polymer particles [6,7]. This calcium complex is hydrophobic in nature and this way the availability of free calcium hydroxide in concrete to be attacked by acid becomes less.

The damage was more pronounced in cut sections than in uncut ones. In the first case the cement mortar is damaged and then the damage comes to the aggregate surface whereas in the latter case the damage occurs directly on the cement paste between the aggregate particles. Moreover, due to the formation of hydroxide layer on the surface of the uncut specimens, the acid penetration was delayed. This is in agreement with the observations made by Romben [8], Dehler [9] and Biczok [10]. The damage of the concrete as observed was in the following order - - normal concrete, then normal concrete with microparticles followed by lightweight aggregate concrete with conventional air entraining agent and lightweight aggregate concrete with micro- particles (3L-concrete).

Sulfuric acid attack The results of concrete deteriora- tion in percent weight loss are produced in graphical form in Figure 1 b. Lightweight aggregate concrete was more damaged by sulfuric acid than the normal concrete. The maximum damage noticed was in the lightweight aggregate concrete with conventional air entraining agent. It looks as if the damage occurred in the case of lightweight aggregate concrete not only on the cementing edges but also on the aggregate. Expansion of cement paste in concrete due to insoluble sulfate might have crushed the lightweight aggregate and increased the permeability of the concrete.

In normal weight concrete it is seen that Cemos did not increase its resistance against acid. This is a surprising result with no explanation at present. The deterioration of concrete as observed was in the following order - - lightweight aggregate concrete with conventional air entraining agent, then lightweight aggregate concrete with microparticles (3L-concrete), followed by normal concrete with microparticles and normal concrete.

Lactic acid attack In the case of lactic acid, growth of some hard, white insoluble material was noted in the matrix between the aggregates. This has given weight

increase of the concrete and this effect is similar to that reported by Dehler [9].

The results of concrete deterioration in terms of percent weight loss are produced in Figure lc. It is evident from the results that minimum damage occurred in the lightweight aggregate with polymer microparticle addition. It seems as if there was some reaction between lactic acid and some component of the cement paste. One of the possibilities is the formation of calcium polylactate, due to the reaction between calcium hydroxide formed during hydration of cement and the lactic acid. This reaction product, which looks white, grows out from the cementing surface creating expansion cracks and is very hard. The destruction as observed was in the following order - - lightweight aggregate concrete with conventional air entraining agent, then lightweight aggregate concrete with microparticles (3L-concrete), followed by normal con- crete and normal concrete with microparticles.

CONCLUSIONS Normal concrete as well as lightweight aggregate concrete are damaged during storage in hydrochloric, sulfuric and lactic acids. The degree of deterioration depends on the type of acid and type of concrete.

Lightweight aggregate concrete with polymer microparticles is more resistant to hydrochloric acid (15% concentration) attack than lightweight aggregate con- crete with conventional air entraining agent. This shows that increase in durability is due to the polymer microparticles and not only due to the entrained air.

Normal concrete with polymer microparticles has shown better resistance to hydrochloric acid (15% concentration) than normal concrete without these microparticles.

Lightweight aggregate with polymer microparticles and with conventional air entraining agent is less resistant to sulfuric acid (5% concentration) than normal concrete without and with microparticles. The light- weight concrete with microparticles is more resistant than the same with conventional air entraining agent.

Lactic acid (5% concentration) showed more severe damage on lightweight aggregate concrete with conventional air entraining agent than on the lightweight aggregate concrete with polymer microparticles.

Normal concrete with polymer microparticles showed better resistance to lactic acid than normal concrete without microparticles.

In general cut concrete specimens were more damaged than uncut ones. The film-forming polymer microparticles increased the resistance to hydrochloric and lactic acid of the lightweight aggregate concrete as well as of normal concrete.

REFERENCES 1. Chandra, S., Berntsson, L. and Aavik, J., 'Influence of

polymer microparticles on freeze-thaw resistance of structural lightweight aggregate concrete', The International Journal of Cement Composites and Lightweight Concrete, Vol. 4, No. 2, May 1982, pp. 111-15.

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Influence of polymer microparticles on acid resistance of structural lightweight aggregate concrete Chandra and Berntsson

2. 'Concrete-polymer materials', Fourth topical report, edited by L. E. Kukacka and G. W. De Puy, Engineering and Research Centre, Denver, Report REC-ERC-72-10 and Brookhaven National Labora- tory, Upton, Report BNL 50328, January 1972, pp. 42 and 102.

3. De Puy, C. W., 'Freeze-thaw and acid resistance of polymer impregnated concrete', Publication SP-47, Durability of Concrete, American Concrete Institute, Detroit, 1975, pp. 233-57.

4. Rubetskaya, T. V., Bubnova, L. S., Gronchar, U. F., Ljuberskaya, G. V. and Fedorchenco, V. 0., 'A method of calculation of depth of destruction in concrete in corrosive conditions', Beton i Zhelezobe- ton, No. 10, October, 1971, p. 3.

5. Chandra, S., 'Frost resistance and other properties of cement mortar with and without admixtures', Chalmers University of Technology, Division of Building Materials, Report 82:3, G6teborg 1982.

6. Chandra, S., Flodin, P. and Berntsson, L., 'Interaction between calcium hydroxide and styrene- methacrylate polymer dispersion', Third Interna- tional Congress on Polymers in Concrete, May 13-15, 1982, Koriyama, Japan, pp. 125-30.

7. Chandra, S., Berntsson, L. and Flodin, P., 'Behaviour of calcium hydroxide with styrene-methacrylate polymer dispersion', Cement and Concrete Research, Vol. 11, No. 1, January 1981, pp. 125-9,

8. Rornb~n, L., 'Aspects on testing methods for acid attacks on concrete - Further experiments', Swedish Cement and Concrete Research Institute, Report FO 9: 1979, Stockholm 1979.

9. Dehler, E., 'Betonzusatzmittel und aggressive Best~ndigkeit von Beton', Betontechnik, No. 3, June 1980, pp. 20-2.

10. Biczok, I., 'Concrete corrosion- concrete protec- tion', Akademiai Kiado, Budapest, 1972, p. 149.

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