Development of cement-based ultra-high strength concrete

Abstract

The utilization of high strength concrete in the modem construction has lead to the remarkable benefits in duration and economics. Toward the workability to assure its strength and performance, the production of concrete with compressive strength greater than 150 MPa is still challenging. The primary objective of this research is to produce such an ultra-high strength concrete by using the commonly-used concrete making materials with the conventional practice. The compressive behavior of concrete is firstly simulated by finite element analysis of triangular basic element. Aggregate particles are randomly generated in bulk matrix with interface. The constitutive relations of each phase are described by using smeared crack concept, on the basis of fictitious crack model. The principal properties of each material component significantly govern the concrete properties and performance. The internal structure of each concrete ingredient, i.e., cement, pozzolanic materials, as well as fine and coarse aggregate, would then be investigated physically, chemically and/or mechanically. The appropriate mix proportion for ultra-high strength concrete is determined by minimizing porosity to obtain the highest strength of proper flow for workable. To obtain this, the optimum water/cement ratio, the suitable addition of pozzolanic materials, and the selection of well-distributed high-strength aggregate are found as the keys. Strength-based gradation, which is also developed in this research, is considered as an influential indicator to qualify the potential coarse aggregate on packing intensity and load-carrying capacity. The eight-step mix design procedure for ultra-high strength concrete is presented. The compressive strength of concrete is calculated by multiplying cement paste compressive strength, which is a function of water/cement ratio, by the coefficients associated with the existence of aggregate and pozzolans. Flowability of the mix is facilitated by using free water concept. With this procedure, a concrete with compressive strength up to 188.30 MPa at 28 days and 203.48 MPa at 91 days can be produced.