Heat of hydration models of cementitious materials

Abstract

Silica fume from certain metallurgical operations, granulated slag from metal industries and fly ash from the combustion of coal are industrial by-products that have been widely used as mineral admixtures in normal-and highstrength concrete. Due to the reaction between calcium hydroxide (CH) and mineral admixtures, the hydration of concrete containing mineral admixtures is much more complex compared with that of Portland cement. In this paper, the production of CH in cement hydration and its consumption due to the reaction of mineral admixtures is considered in order to develop a numerical model that simulates the hydration of concrete containing silica fume, fly ash or slag. The heat evolution rates of these admixture-blended concrete were determined by the contribution of both cement hydration and the reaction of the mineral admixtures. The proposed model was verified with experimental data on concrete with different water/cement ratios and mineral admixture substitution ratios. IntroductionMineral admixtures (fly ash, silica fume and slag) are usually added to concrete to enhance the workability of fresh concrete, to improve resistance to thermal cracking, alkali-aggregate expansion and sulfate attack, and to enable a reduction in cement content. The utilisation of by-product mineral admixtures not only improves concrete properties but also reduces concrete cost and environmental problems (Mehta and Monteiro, 2006;Taylor, 1997).In hardening massive concrete elements, the heat of hydration gives rise to considerable thermal gradients and thermal stresses, which may cause early-age cracking. A cogent simulation of an exothermic hydration process in cement plays a crucial role in quantifying thermal stress and assessing the risk of thermal cracking in mass concrete. Tomosawa et al. (1997) proposed a hydration model to estimate the heat liberation rate during the hydration of Portland cement and the adiabatic temperature rise in concrete. In this model, the residual concentration of water is used as a parameter indicating the decline of the reaction rate towards the reaction end point. The influence of temperature on cement hydration is considered by the Arrhenius law. Based on Tomosawa's model, Park and co-workers (Park, 2001;Park et al., 2008) constructed a microstructural hydration model of Portland cement that considers the reduction in the hydration rate that occurs due to the reduction of free water and the reduction of the interfacial area of contact between the free water and the hydration products. Based on a hydration model using a finiteelement method, the temperature distribution of high-strength concrete was evaluated. Swaddiwudhipong et al. (2002) proposed a multi-constituent model of Portland cement hydration by combining the multi-component model of Kishi and Maekawa (1996) with the hydration model of Parrot and Killoh (1984). The concept of equivalent maturity is introduced explicitly to reflect the influence of temperature on the rate of hydration heat release.Compared with Portland cement, the h...

Calorimetric Studies of Alkali-Activated Blast-Furnace Slag Cements at Early Hydration Processes in the Temperature Range of 20–80 °C

“…Alkali activated cement is characterized by low and almost similar heat release values obtained also by thermochemical and thermokinetic experiments. The results are also interesting in assessing and considering the heat released in the process of cement hydration in the production of concretes from them [ 31 , 32 ].…”

Cement Hydration Rate of Ordinarily and Internally Cured Concretes

“…For concrete with additional cementitious materials used, the total hydration heat of cement may differ from (3). Existing studies show that the use of silica fume (SF) and fly ash (FA) will influence the total hydration heat of cement (Kishi and Maekawa 1995;Schindler et al 2005;Maekawa et al 2009;Wang et al 2012). Based on the results of the contribution of fly ash and silica fume to the total hydration heat of cement presented by Kishi and Maekawa (1995) and Maekawa et al (2009), for concrete with fly ash and silica fume used respectively, equation 3is revised as (4) to take the effect of the additional cementitious materials on cement hydration heat into account in the present study.…”

A new hydration kinetics model of composite cementitious materials, Part 2: Physical effect of SCMs

“…Nowadays, an increasing amount of supplementary cementitious materials (SCMs) have been used in the preparation of cement concrete, eg, fly ash, steel slag, silica fume, and ground granulated blast furnace slag (GGBS) . In addition to the chemical reaction, these mineral admixtures also have some impacts on the early hydration of cement due to their physical presence which is generally named as filler effect .…”

“…Nowadays, an increasing amount of supplementary cementitious materials (SCMs) have been used in the preparation of cement concrete, eg, fly ash, 2-6 steel slag, [7][8][9][10][11] silica fume, 4,[12][13][14][15] and ground granulated blast furnace slag (GGBS). 13,[16][17][18][19] In addition to the chemical reaction, these mineral admixtures also have some impacts on the early hydration of cement due to their physical presence which is generally named as filler effect. 20,21 The filler effect of SCMs has been widely studied and it is generally presented in the first day of hydration when the microstructures and properties are rapidly developing.…”