Development of Strength vs Water-Cement Ratio Graphs for Normal Concretes Made with Various Types of Local Cements and Proposing a Mix Design Method for Pakistan

Abstract

The w/c ratio-strength relation plays a key role in selection of an adequate recipe against a particular target strength of concrete with and without admixtures. The relation proposed by American Concrete Institute (ACI) for normal concrete using ordinary Portland cement (OPC) is frequently used in Pakistan as a definite rule to decide the mix contents. However it is observed that in some cases, the desired strength is not achieved while using ACI method of mix proportion with locally available materials and the mix needs to be adjusted several times later on. This research has investigated the applicability of previous internationally established or proposed w/c-strength relations of concrete systems in Pakistan. Various charts and graphs are designed using relevant computer software packages for convenient and handy use of results. Detailed strength testing on various types of concrete specimens (with different local cement types and other ingredients) is carried out according to International standards in order to develop a consistent relation between w/c and compressive strength for locally available aggregate and cement types and to address the absence of data regarding adjustments to trial batches while selecting a suitable proportion against strength, workability and resistance to segregation and bleeding. Empirical equations for w/c ratio – Strength relations are proposed for all available cement types and have been checked subsequently in order to comment on accuracy of their prediction against target strength. A wide range of other variables including maximum aggregate size, fineness modulus and percentage of fine aggregates, super plasticizer dosage, splitting tensile strength and elastic modulus are also considered in the study for assessing the validity of various International code provisions regarding these parameters. Based on these relations, a method of mix proportion is proposed and a computer software is developed in MATLAB GUI Environment in order to ensure the practicality and convenience in using the method in Pakistan for the benefit of end users including Postgraduate students, Professional Engineers, Consultants and concrete plant managers.