IOSR Journal of Applied Chemistry (IOSR-JAC) e-ISSN: 2278-5736.Volume 9, Issue 1 Ver. I (Jan. 2016), PP 11-15 www.iosrjournals.org DOI: 10.9790/5736-09111115 www.iosrjournals.org 11 |Page Effect of sulphate ions in mixing water on cement mortar performance Munyao Onesmus Mulwa 1 , Thiong’o Joseph Karanja 2 and Muthengia Jackson Wachira 3 1 Chemistry Department, Kenyatta University, Kenya. 2 School of Pure and Applied Sciences, Embu University College, Kenya. Abstract: The effect of sulphate ions in mixing water on performance of cement mortar was investigated. Mortar prisms were made using selected Portland Pozzolana cement and Ordinary Portland cement with sewage, swampy and bore-hole waters, commonly used as mix waters in most peri-urban set up in Kenya. Potable tap water was used as a control. Compressive strength was determined at 2 nd , 7 th , 28 th , and 90 th day of curing. Setting time was also investigated. Results showed that sewage and swampy mix waters had significant sulphate content. The sulphate ions reduced the early compressive strength development of cement mortar in both PPC and OPC. Further, sulphate ions retarded both initial and final setting times in PPC and OPC. The use of sewage and swampy waters as mix water containing high sulphate ions could lead to failure of concrete and/or mortar and hence building and construction. Key Words: Cement Mortar, Mixing water,OPC, PPC, Sulphate ions. I. Introduction Mixing water is very vital for development of concrete and /or mortar. It can also be a source of aggressive ions in the cured concrete/ mortar [1]. In Kenya, there are no legal standards on the quality of mixing water for cement mortar/ concrete. Further, there are no controls on quality of mixing water. Water is majorly scarce in Kenya and therefore, majority of construction workers use any available water for mixing concrete/mortar. The presence of impurities in mixing water not only affects setting time and strength development of mortar/concrete, but also causes efflorescence, staining, corrosion of reinforcement, volume instability and reduced durability [4]. Presence of sulphate ions in many water masses makes them readily available to cement matrix either during cement paste making or to constructed cement structures [2]. The ingress of these ions into cementitious material exposes building into a durability threat [3]. The principal effect of sulfate attack is to reduce the service life of the mortar and /or concrete structures due to degradation. Sulfate attack results in expansion, cracking, spalling and eventually reduce strength of concrete [5, 6, 7]. Mixing water rich in sulphate ions result into an internal sulphate attack [8, 9]. Sulfates react with the aluminium-containing phases of Portland cement mortar paste causing internal expansion [10, 11, 12]. The expansion is attributed to formation of expansive products such as thaumasite, ettringite and gypsum as shown in equations (1) - (3) respectively. O 2 .15H 3 .SO 2 .CO 2 3CaO.SiO O 2 5H 2 4 SO 2 3 CO 2 3 SiO 2 3Ca          ………………........ (1)   O 2 .32H 4 .3CaSO 3 O 2 3CaO.Al O 2 26H 3 O 2 3CaO.Al O 2 .2H 4 CaSO 3    ……………………….. (2)   O 2 .2H 4 CaSO 2NaOH O 2 2H SO4 2 Na 2 OH Ca     ……………………………………………..(3) The study investigated the effect of sulphate ions in mixing water commonly used in peri – urban set up in Kenya. Hence, it is expected that this work would help to establish a clearer guidance on identifying suitable water for mixing concrete/ mortar and also help contractors to safe water sources for their construction works.