Inﬂuence of cement ﬁneness and water-to-cement ratio on mortar early-age heat of hydration and set times Jiong Hu a,⇑ , Zhi Ge b , Kejin Wang c a Department of Engineering Technology, Texas State University, 601 University Drive, San Marcos, TX 78666, United States b Department of Transportation Engineering, School of Civil Engineering, Shandong University, 17923 Jingshi Road, Jinan 250061, China c Department of Civil, Construction, and Environmental Engineering, Iowa State University, 492 Town Engineering Building, Ames, IA 50011, United States highlights  Studied the inﬂuence of cement ﬁneness on heat of hydration.  Studied the inﬂuence of water-to-cement ratio on heat of hydration.  Developed heat indexes to quantify heat of hydration process.  Developed an innovative procedure to predict set times from calorimetry test.  Compared set time predicted from the calorimetry method to the ASTM set time test. article info Article history: Received 19 July 2013 Received in revised form 28 September 2013 Accepted 4 October 2013 Available online 5 November 2013 Keywords: Hydration Calorimetry Isothermal Water-to-cement ratio Fineness Set time abstract In this study, hydration of mortars containing portland cement of three different ﬁnenesses and prepared at four different water-to-cement ratios (w/c) were investigated using isothermal calorimetry tests. Results showed that the hydration heat generated from cement with higher ﬁneness was larger and faster compared to coarser cements in early ages. The lower w/c resulted in a higher heat of hydration rate at earlier hours but reduced after that. While the maximum heat of hydration rate was lower with higher w/c, total heats of hydration within the ﬁrst 24 h were found to be approximately the same, regardless of the different w/c used. Initial and ﬁnal set times determined from isothermal calorimetry were found to relate to set times determined from ASTM C403 penetration tests. The set times increased with the increasing of the w/c and decreasing of the cement ﬁneness. However, due to the very different mecha- nisms and test setups in determining setting times, the relationship between these two methods may vary among different cements. Longer setting times were generally obtained from the calorimetry method compared to the ASTM set time test. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Recently, activities and interests in monitoring heat evolution from cement hydration in portland cement concrete have dramat- ically increased. The development of early-age concrete properties, such as workability, setting time, strength gain and thermal crack- ing resistance, are predominantly inﬂuenced by the kinetics of ce- ment hydration [1]. Hydration of cementitious materials in a concrete mixture results in a number of exothermic chemical reac- tions that liberate heat [2]. The heat evolution process is strongly inﬂuenced by the chemical and physical properties of portland ce- ment, water-to-cement ratio (w/c), mineral and chemical admix- tures, concrete mix proportions, construction procedures and curing conditions of concrete [3–8]. As a result, deviations in the quantities and characteristics of the concrete constituents, as well as effects of construction conditions, can be detected [9]. Concrete performance can also be predicted by monitoring the heat of ce- ment hydration [10,11]. Different calorimetry test methods have been developed to monitor cement hydration over time [12–15]. The calorimetry pro- cedure has also been termed as the heat signature or thermal ﬁn- gerprint test since it measures a heat/temperature-related property that is unique to a given concrete mixture. From a purely theoretical standpoint, there are two major types of calorimetry tests: semi-adiabatic and isothermal. In a semi-adiabatic calorime- try test, the heat of hydration is measured by monitoring the tem- perature of a specimen while the specimen is under an insulated condition and has minimal heat loss. The isothermal calorimetry test, on the other hand, measures the heat ﬂow from a specimen while both the specimen and surrounding environment are main- tained at approximately the same constant temperature. Previous 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.011 ⇑ Corresponding author. Tel.: +1 512 2456328; fax: +1 512 2453052. E-mail address: jiong.hu@txstate.edu (J. Hu). Construction and Building Materials 50 (2014) 657–663 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat