Sulphate And Chloride Ingress And The Effect In Selected Cements Mortar Prisms Immersed In Sea Water And Leather Industry Effluent

ABSTRACT

The effect of ingress of Cl- and SO4

2- on compressive strength development and the ions

diffusivity in selected Ordinary Portland Cement (OPC) was investigated. The aggressive

media used included sea water (SW) and waste water from leather industry (WLI). Three

brands of commonly used cements of OPC in Kenya were used. Mortar prisms were

prepared for each brand of cement at different water to cement ratio; (w/c) of 0.5, 0.6, 0.65

and 0.7 and allowed to cure for 28 days in a highly humid environment. The aggressive

ions ingress in the mortar prisms was accelerated using a potential difference of 12V ±

0.1V DC power source. Analysis of diffusivity and diffusion coefficient of Cl- and SO4

2-

was finally done. Compressive strength analysis was done before (at the 2nd, 7th, 14th and

28th day) and after exposure to the aggressive ions. The diffusivity of chlorides was more

pronounced than that of sulphates. Diffusivity was observed to be higher at higher w/c for

all cement categories. The apparent diffusion coefficients (Dapp) of chlorides were found to

be higher than those of sulphates. Dapp values for chlorides were found to be in the range

of 1.730 x 10-10 m2/s to 4.683 x 10-10m2/s and for sulphates within 1.0610 x 10-11 m2/s to

6.2240 x 10-11 m2/s. The Dapp values were approximated from solutions to Fick’s 2nd law

using the error function. Cement A at all w/c showed lower Dapp values than both cements

B and C. Compressive strength increased with curing age with the highest observed at 28

days. Cement A was generally found to have the highest compressive strength for all w/c

ratios. The compressive strength was observed to increase after the mortar prisms were

exposed to SW as opposed to the ones exposed to WLI. The percent gain in compressive

strength was found to increase with increase in w/c with the highest observed to be about

38 % at 0.7. The percent loss in compressive strength also increased with w/c with the

greatest observed to be about 17 %. Generally, it was also observed that compressive

strength gain / loss increased with increase in w/c.