The concrete mixes used in this study had 28 d mean strengths of 50 and 30 MPa and also had Portland cement (PC) partially replaced with ground granulated blast-furnace slag (GGBS) and fly ash (FA). These mixes were the same as those used in a UK-based project that involved casting of blocks, walls and slabs. The strength development of ‘equivalent’ mortar mixes was determined in the laboratory for curing temperatures of 10, 20, 30, 40 and 50°C. High curing temperatures were found to have a beneficial effect on the early-age strength, but a detrimental effect on the long-term strength. GGBS was found to be more sensitive to high curing temperatures than PC and FA, as reflected in its higher ‘apparent’ activation energy. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse–Saul function (i.e. concrete strength gain rate varies linearly with temperature) was not sufficient to account for the improvement in early-age strengths resulting from high curing temperatures. The Arrhenius-based function, on the other hand, overestimated them because of the detrimental effect of high curing temperature on strength starting from a very early age. Both functions overestimated the long-term strengths, as neither function accounts for the detrimental effect of high curing temperatures on the ultimate compressive strength.

Effect of in situ temperature on the early age strength development of concretes with supplementary cementitious materials Soutsos, M., Hatzitheodorou, A., Kwasny, J., & Kanavaris, F. (2016). Effect of in situ temperature on the early age strength development of concretes with supplementary cementitious materials. Construction and Building Materials, 103, 105-116. DOI: 10.1016/j.conbuildmat.2015.11.034 General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. AbstractA UK based project which involved casting of blocks, walls and slabs, during winter and summer, provided in situ temperature histories that could be simulated in the laboratory using a computer controlled temperature match curing tank. The concretes which were of 28-day target mean strengths of 50 and 30 MPa also had partial cement replacement with supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA). The SCMs were effective in reducing the peak temperature especially when there was heat dissipation.The contribution to early age strength by SCMs increased with the high in situ temperatures especially in blocks cast during summer. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse-Saul function was not sufficient to account for the improvement in early age strengths resulting from the high temperatures in blocks cast during summer. The Arrhenius based function, was better at estimating the early age strengths as it assumes that the concrete strength gain rate varies exponentially with temperature.

This paper is the joint work of working group 4 of the RILEM TC 238-SCM and the fib Task Group 4.6. It was the aim of this literature study to quantify the effect of ground granulated blast furnace slag (GGBS) and silicious fly ash (sFA) on strength development of concrete. For the strength development the approach of the fib Model Code was chosen, which is based on an e-function that can be adapted to the strength development of an individual binder by selecting the so-called s-value based on the strength class of the Portland cement used. No guidance is provided for s-values for supplementary cementitious materials (SCMs). In order to determine the s-values for mixes with SCMs, a database was set up with results of material testing from literature. A relationship between s-values and w/b plus SCM/b ratios has been determined. This has been tested on laboratory cast specimens with 50 and 30 % cement replacement with GGBS and FA respectively. These were cured at 20 0 C. The s-values from this relationship were compared to those obtained from regression analysis and they were found to be satisfactory. This increased confidence in their use for predicting the strength development of other curing regimes, i.e. adiabatically cured concrete cubes, using the maturity function in the fib Model Code. Predictions of the effect of curing temperature, i.e. the adiabatic temperature history, on the strength development were again satisfactory. These were not significantly affected by the fib model code's use of one value of "apparent" activation energy.

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Cracking occurrence due to shrinkage related effects is a widely recognised issue which is frequently evaluated with the shrinkage restraining ring test. This paper provides a state-of-the-art review of the ring test method, which has been used for the last four decades. The last review on such matter was conducted only in early 2000s; however, a significant amount of studies has been conducted since then and considerable advancements or modifications in this testing method have taken place over the last decade. Studies on the traditional ring test, i.e. a circular concrete ring cast around a steel ring, are identified and the history, tendencies, practices and quantitative methods are analysed thoroughly. Furthermore, any modifications/advancements in the testing method with respect to their purpose, applications and capabilities based on current knowledge, are addressed. Finally, an insight on the challenges that the developers of testing methods for restrained shrinkage are facing with is given together with perspectives for their future potential improvement.