The effects of ions on mortar cubes made with Kenyan cements and sands

Abstract

A study of the effects of aggressive solutions on mortar cubes made from Kenya~ cements and sands has been conducted. The study is important because failure of concrete structures exposed to rain water, domestic and industrial effluents is increasing. Ordinary portland cement; sulphate resisting portland cement; and pozzolanic cement were used to make 70.7 mm cubes with British Standard sand and suitable sand samples from Kajiado and Machakos districts. The cubes were imme~sed in: deionised water; waste water from a facto~y; two concentration solutions of fluoride, ch~oride and sulphate prepared from the respective aci~s. The effect of the soluLions on the cubes for a .eriod of six months was monitored by measuring volume changes and compressive strengths of t~e cubes; pH, anionic and cationic concentrations of Lhe solutions. The results for the cubes made with the standard sand were use~ to assess the perfo~~ance of the cements. The performance of the sands was assessed by holding the different cements constant i~ the tests. Ka-j iado sand has been fOI....d.:t.o be more coarse and to contain more silt than ~~e ~achakos one. Machakos sand, on the other hand, has been found to be richer in mineral content. Quartz has been found to form the bulk of the two sands. Machakos sand has been found to form unworkable mixes with cements when using a W/C ratio of 0.4, and to bulk when using a W/C of 0.5. The waste water from the factory has been found to contain the following levels of anions: sJlphates 361.8-2566.5 ppm; chloride 298.2-1498.8 ppm; fluoride 5.5-38.9 ppm; and phosphate 0.306-1.224 ppm. The solutions have been found to affect the cubes differently. In environments rich in sulphate ions but combined with other ions, like iGdustrial effluents, sulphate resisting portland cement should be used only after 2 careful study. The reactions of the cubes with The fiuoride solutions have been found to be less deleterious than with the other ions investigated and in some cases fluoride ions were beneficial. The c~~ent-sand combinaTions That ~ere found to have TJerfY--med-...Jeilnl the d i f f er-e rrt environments are: