Strength behaviour of clay-cement concrete and quality implications for low-cost construction materials

Abstract: Incorporation of clay soil into concrete mixtures may be one means of designing low- cost, low strength construction materials but its influence on material properties should be understood as it affects engineering performance. This paper argues that the use of concrete for low-cost cementitious building mate-rials has special requirements. A significant demand exists for physical infrastructure in developing countries (DCs), and concrete or mortar blocks of sufficient integrity for low-cost housing, for instance 2 MPa, are of-ten made from cement with clay-contaminated sand by artisanal builders. The work presented is based on the experimental results of a laboratory study done for clay-cement con-crete material. The clay-cement concrete studied was designed to be a low-strength material and its properties fall between those of soil and concrete. Four control concrete mixtures of 350 kg/m3 CC (cementitious con-tent) of w/cc (water – cementitious ratio) = 0.70, 0.75; 280 kg/m3 CC of w/cc = 0.80, 0.85 were prepared. Fur-ther mixtures were made by substituting the OPC (ordinary Portland cement) in control mixes with 10, 20, 30, 40, and 60% local raw clay. Compressive strengths were measured at ages of 7, 28, 56, 270, and 365 days for all the mixtures. The laboratory test results show that clay-cement concrete mixtures with a maximum of w/cc = 0.80 and 20 to 30% clay replacement can be suited to fulfill the requirement of strength and workability for low–cost, low strength applications including housing, roads and dams which are current important social and economic issues of concern in DCs. Interestingly, clay-cement concretes gave higher strength performance factors at later ages than the corresponding plain cement concretes, suggesting a possible pozzolanic be-havhiour, however minimal. Further investigations are being undertaken to determine the behavior of the clay-cement mixtures through study of drying shrinkage, creep, abrasion resistance, and fluid permeability