Strength and shrinkage properties of alkali-activated slag concrete placed into a large column

The properties of alkali-activated slag concrete (AASC) are generally determined on small-scale laboratory-produced prisms or cylinders. This investigation reports the in situ strength and in situ strain results from measurements on an 800 X 800 X 1200-mm column composed of AASC produced at a concrete plant. The results are contrasted with those of columns made with ordinary portland cement (OPC) and blended cement (50% OPC + 50% slag) designated as GB50/50. For this type of AASC, the workability improved from the time of production to the time of concrete placement and minimal slump loss occurred over 2 hours (in contrast with OPC). The rate of in situ temperature development was similar to GB50/50, and slower than OPC; however, the maximum temperature difference between the interior and the exterior was considerably less than OPC and GB50/50, The in situ strength was identical to OPC and superior to GB50/50 at 28 and 91 days. Embedded strain gauges show small initial in situ expansion within the centre of the column followed by a rapid rate of tensile strain growth up to 14 days. At 91 days the differential strain between the centre of the column and the corner was sufficient to crack OPC concrete; however, the AASC column remained uncracked. Possible explanations for this behaviour could be due to a greater tensile strain capacity of AASC than OPC concrete caused by greater creep and lower elastic modulus and higher tensile strength of AASC. (C) 1999 Elsevier Science Ltd. All rights reserved.