Properties of Portland Cement Concretes Containing Possolanic Admixtures

摘要

A laboratory comparison was made of the properties of a concrete containing no pozzolan with several mixtures containing pozzolans. Used were a natural pozzolan (Lassenite), two fly ashes of different fineness and low carbon and an amorphous silica fume dust from a metal-producing plant. The no-pozzolan mixture had a cement factor of 564 lbs per cubic yard, a water to cement-weight ratio of 0.53, a slump of 3 inches, 6 percent air and a compressive strength of approximately 4500 psi at 28 days. One cement, one coarse crushed limestone aggregate, and one fine river aggregate were used. The basic mixture was modified in three schemes: a 15 percent equal volume replacement of pozzolan for cement, a 25 percent similar replacement, and a 2 for 1 replacement of pozzolan for cement, whereby 13 volume percent was replaced by 26 percent pozzolan with the extra volume compensated for by removing fine aggregate. The concretes were compared for the amount of air entraining agent, compressive and tensile splitting strengths, modulus of elasticity, drying shrinkage, skid resistance, abrasion resistance, scaling resistance, freeze-thaw durability, chloride permeability, and outdoor exposure. Evaluations were done at equal ages and at approximately equal strengths. Replacing a faster reacting binder with a slower one, produced lower early strengths and adversely affected the properties which are highly dependent on strength. The measures of durability were greatly affected by the air contents and aging or treatment prior to exposure. The amorphous silica fume dust increased the early strengths of a fly ash mixture.