A study of the effect of calcium sulfoaluminate cement on the structural properties of concrete

Abstract

This research study is to explore the effect of Calcium Sulfoaluminate Cement (CSAC) on the structural properties of concrete when being used as the key binder in combinations with Ordinary Portland cement (OPC), Pulverized Fuel Ash (PFA) and Ground Granulated Blastfurnace Cement (GGBS). Following the increasing use of CSAC in structural concrete applications utilizing its characteristics in early strength and/or low shrinkage, there are needs for obtaining more knowledge of its structural properties in comparison with conventional concretes incorporating OPC, PFA and GGBS only. Structural properties of CSAC concretes studied in this research are the development trends of compressive strength (from a few hours to 1 year) and shrinkage (from early to ultimate stage) as well as its fire resistance performance represented by strength reduction after exposure to elevated temperature. Experimental approach was adopted to obtain test results from a total of 20 concrete mixes were studied for analysis, based on which conclusions are made for the development trends of CSAC concretes in strength and shrinkage up to the age of one year. Reduction in strength at 28 days after exposure to an elevated temperature of 300°C are also collected for comparison with those given in current design codes. Based on predicting models developed in previous literatures for conventional concretes using OPC as the key binder, new models for predicting the strength development of CSAC concretes of various binder combinations with OPC, PFA and GGBS are established for enabling engineers to easily estimate the strength performance of such concretes while long period trial tests are often impractical. Similarly, prediction models for shrinkage of concretes using OPC are currently available in well-recognized literatures but not covering concretes incorporating CSAC in binder combination. By using the test results obtained in this study, correction factors for various binder materials other than OPC are derived for putting in the widely adopted GL2000 Model given in ACI 209.2R-08: "Guide for Modelling and Calculating Shrinkage and Creep in Hardened Concrete". With the newly derived correction factors, the applicability of the GL2000 Model is broadened to cover concretes with various binder combinations of CSAC, OPC, PFA and GGBS. Strength reduction factors after exposure to elevated temperature of 300°C for concretes incorporating CSAC were also obtained in the study for evaluating the fire resistance of concretes incorporating CSAC. Lastly, rapid strength development and volume stability characteristic of pure CSAC concrete at early ages and its ability to achieve similar long-term strength as that of pure OPC concrete are confirmed. Effects of combining CSAC with PFA and GGBS in terms of development of strength and shrinkage as well as the fire resistance represented by reduction in strength after exposure to elevated temperature were concluded. Based on the study results, limitations of applicability of results obtained in this study and the use of CSAC concrete in structural applications are given. Further studies on more properties of CSAC concrete in comparison with conventional OPC concrete incorporating commonly used supplementary binder materials of PFA and GGBS are suggested.