ABSTRACT
Conventional concrete is porous and the network of pores allow the passage of harmful substances through the concrete internal structure thereby causing damage to the internal structure of the concrete and which resulted in consequential loss of concrete durability. Efforts have been made to protect concrete but problem still exist such as in adequate protection and high cost of protection in view of the drawbacks this research work investigates effects of permeability reducing admixture on thedurability properties of binary cementitious matrix concrete.A total of 342 sample specimens of 100mmx100mmx100mm cubes were cast with the following connotations, 100% cement, 2% PRA, 10% C S A, 15% C S A, 2% PRA + 10% C S A and 2% PRA + 15% C S A, The permeability reducing admixture was purchased from Market, The coconut shell was pre ashed in an open air for one hour and was allowed to cool then calcined at temperature of 8000C in a kiln for 4hours and was allowed to cool to room temperature before it?s removal from the kiln, the Coconut Shell ash was used to replace cement at 10% and 15% replacement. 90 specimens were tested for compressive strength, 90 specimens were tested for compressive strength in aggressive environment (MgSO4), 162 specimens were tested for water absorption capacity, sorptivity and abrasion resistance. The plain concrete, the plain concrete modified with PRA, Blended concrete and Blended concrete modified with PRA were cured in water and their respective properties were evaluated at 14, 28, 56, 90 and 180 days curing period respectively. The control sample had the highest compressive strength test of 33.85N/mm2 at 28 days, however at 56 days all the samples exceeded the control in strength except 15% CSA that had 32.95 N/mm2, at 90 and 180 days all the samples exceeded the control, Ninety samples were immersed in aggressive media i.e exposure to 2.5% magnesium sulphate solution, compressive strength was used to determine the severity of the effects of MgSO4on concrete samples, at 90 days all the samples loss strength but the loss was more severe in control sample, the control loss 17.7% of its strength, 2% PRA loss 1.6% , 10% CSA loss 3.8% at 90 days, 15% CSA loss 4.75% at 90 days, 2% PRA+ 10% CSA loss 1.0% and 1.3% of its strength at 90 days, 2% PRA+ 15% CSA loss 0.76% at 90 days, at 180 days it was discovered the effect was more severe on control samples and less severe on all other samples, absorption capacity test revealed that the PRA modified Pozzolana blended cement concrete had the lowest water absorption of 0.87% at 90 days, the PRA modified Pozzolana blended cement concrete had the lowest sorptivity of 0.62 at 90 days. Based on the above findings it was concluded thatPRA modified pozzolana blended cement concrete is most durable, then it was recommended that it could be used for concrete production in soil that its Magnessium sulphate content is high and where concrete may be subjected to water ingression.