COMPRESSIVE STRENGTH ASSESSMENT OF CONCRETE WITH DIFFERENTNALKALI-ACTIVATED POZZOLLANS AND 15 TO 20% REPLACEMENT OF SAND WITH LATERITE

Abstract

The ever increasing rise in the cost of cement and the threat on the environment during its production have led to the continuous search for alternative binding materials in its place. Researchers have been looking into the possibility of harnessing both artificially and naturally occurring materials to partially or wholly replace cement in the construction industry. Materials such as slag, fly ash, wood ash and corncob ash which have cementitious properties, have been investigated, while works have been intensified on the use of metakaolin, rice husk ash, palm oil fuel ash as cementitious materials in the last decades. This work looked into how best Alkaliactivated pozzolans like metakaolin, rice husk ash and palm oil fuel ash can be blended together to replace cement partially in varying proportion and at the same time, 15% and 20% by mass of sand was also replaced with laterite. Cement, sand and granite were mixed in the ratio of 1:2:4 to serve as control test. It was on this platform that the Alkali-Activated Pozzolans were blended with cement by replacing cement with Alkali-activated pozzolans up to 40% and also sand with laterite up to 20% by mass of cement and sand respectively. The Alkali used are Sodium Hydroxide (NaOH) and Sodium Silicate (NaSiO3) in ratio 1:2.5 while Alkali/Pozzolan were mixed in the ratio of 1:2. Chemical tests were conducted on the selected materials and the results showed that they all have pozzolanic characteristics. The compressive strength tests revealed that cement can be partially replaced in concrete with the blend of Alkali-activated pozzolans (metakaolin, rice husk ash and palm oil fuel ash) for up to 40% by mass of cement with laterite replacing sand for up to 20% by mass of sand with the water/cement ratio of 0.5 and 0.65. For instance, at 7 and 28days, the compressive strength test on concrete mixed in ratio 1:2:4 of cement, sand and granite at w/c ratio of 0.5 gave 10.30N/mm² and 17.52N/mm² respectively. However, on replacing cement with Alkali-activated Pozzolans of 5% Metakaolin (MK), 5% Rice Husk Ash (RHA) and 15% Palm Oil Fuel Ash (POFA), termed MR5, P15, and replacing sand with 15% laterite at 0.5 w/c ratio, 9.15N/mm² and 15.5%N/mm² compressive strength were obtained at 7 and 28days respectively. At 60days, more strength was gained by the mix with Alkali-activated Pozzolans than the mix without Alkali-activated Pozzolans (control) in that the compressive strength of the MR5, P15 rose to 17.10N/mm2 whereas the compressive strength of the control just increased slightly