Curing of slag concretes at low temperatures: effect on selected durability properties
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.154
Curing of slag concretes at low temperatures: effect on selected durability properties Mike Otieno1 and Riccardo Opeka2 1 2
School of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg Calibre Civil & Structural Engineering, Johannesburg
Abstract
The influence of low curing temperatures (5, 10 and 15 r 2 °C) on the strength and durability properties of ground granulated blastfurnace slag (GGBS) and ground granulated Corex slag (GGCS) concretes was studied. A standard curing temperature of 23 r 2 °C) was also used for comparative purposes. Test specimens were cast using 100% CEM I 52.5N (PC), and three PC/Slag (GGBS or GGCS) replacement ratios of 50/50, 65/35 and 80/20, and a w/b ratio of 0.40. The specimens were cured for 28 days by submersion in water at the respective curing temperatures and then tested for durability. Durability was assessed using oxygen permeability, water sorptivity and chloride conductivity tests. The results showed that durability of the concretes decreased as the curing temperature decreased – gas permeability and water sorptivity increased while chloride resistance decreased. It was also observed that at a given curing temperature, the slag blended concretes showed superior durability performance than the plain PC concretes. Corresponding author: Mike Otieno ([email protected])
INTRODUCTION Curing plays an important role in concrete production; it sustains the hydration of cement which is critical for the microstructural development in concrete and pore solution chemistry among other concrete properties. These properties of concrete affect both strength and durability properties of concrete. It is therefore important that curing is implemented as required. This involves provision of suitable moisture and temperature conditions for a given duration of time [1-3]. Provision of adequate moisture and optimal temperature during the curing process should be considered as mutually inclusive if the 1267
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strength and durability potential of concrete is to be realized. Compared to pre-cast concrete production, temperature is difficult, if not impossible, to control in in-situ concrete production, and usually follows the ambient temperature. For this reason, guidelines are available for in-situ concrete production with respect to temperature and minimum curing periods which are in some cases related to the cement type and ambient temperature; for example, South African National Standard SANS2001-CC1 [4] gives guidelines to this effect; it states that “Under adverse cold weather conditions, effective measures shall be taken to ensure that the temperature of the concrete, from time of placing until it has hardened (i.e. about 24 h), is maintained at not less than 5
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