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Concrete In Australia : March 2012
22 Concrete in Australia Vol 38 No 1 FEATURE: CEMENT TECHNOLOGIES temperatures and quicker rates of hydration when tested under isothermal calorimetry at 20 ˚C compared to control paste. At higher water-to-solids ratios, the hydration began earlier but did not reach the same amount of heat as the control. 4.4 Strengths and elastic modulus 4.4.1 Compressive strengths e compressive strength of concrete made using limestone cements is not solely dependent on whether the limestone is interground, the method of manufacture for this research, but on the quality of the limestone and the particle size distribution of the final cement. For cements with up to 5% limestone addition researchers have reported an increase in the early strength due to improved particle packing (Sprung & Siebel, 1991). Increased early hydration according to Bonavetti et al (2003) was possibly due to the formation of nucleation sites that initiate hydration, while Vogilis et al (2005) ascribed it to the early formation of calcium carboaluminates. e general consensus has been that for limestone additions greater than 5% the cement needs to be more finely ground to compensate for the clinker dilution effect. With respect to concrete made with limestone cements containing up to 15% limestone additions the report by Hooton et al (2007) supported the statement by Tsivilis et al (1999a) "... that the appropriate choice of clinker quality, Series A Series B Series C w/c ratio 0.78 0.80 0.45 0.40 Proportions (kg/m3) SCM Nil Nil Nil Nil Nil Nil Portland cement 235 354 -- 409 -- Portland limestone cement 235 -- 358 -- 413 Water 184 188 159 161 164 165 Fresh Properties Air (%) 1.5 1.4 6.2 5.3 6.2 5.4 Slump (mm) 120 115 120 120 130 115 Set time (min) 340 310 340 290 395 355 Table 1: Concrete mix proportions and fresh concrete properties -- study 2 from Thomas & Hooton (2010). Figure 2. Setting time of concrete -- CCAA investigation.