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This paper presents results regarding the effect of elevated temperature (ET) curing on the compressive strength and electrical resistivity of concrete with slow-reacting supplementary cementitious materials (SCMs). Concrete mixtures with Class F fly ash (FA), ground-granulated blast furnace slag (GGBS), or both were tested. Elevated temperature (ET) curing (in a 36°C [97°F] lime water bath) and room-temperature (RT) curing (in a 21°C [70°F] lime water bath) with different durations were investigated. Test results show that the ET curing method can be employed to achieve the specified 28-day compressive strength and resistivity values on concrete with slow-reacting SCMs without compromising the long- term strength and resistivity properties. It is also shown that the use of granite as coarse aggregate as an alternative to limestone can increase concrete's electrical resistivity but has a modest adverse effect on the compressive strength of not fully hydrated concrete.
Keywords: compressive strength; electrical resistivity; elevated tempera- ture curing; SCMs.
INTRODUCTION
Concrete with supplementary cementitious materials (SCMs) usually has enhanced long-term compressive strength and durability properties (for example, resistance to chloride penetration). However, concrete incorporating slow-reacting SCMs (such as Class F fly ash [FA] and ground-granulated blast-furnace slag [GGBS]) usually shows lower compressive strength and higher chloride permeability properties at early age.1-4 Quality-control tests, such as the compressive strength test and rapid chloride permeabilty (RCP) test,5 are usually performed at 28 days, which is often not a long enough time for concrete with FA or GGBS to reach the specified strength or chloride perme- ability properties. Although ASTM C12025 allows the RCP test at 56 days or 3 months for concrete with slow-reacting SCMs, accelerated curing methods are highly desirable to reduce the test time and to increase the production efficiency.
Elevated temperature (ET) curing has traditionally been an effective method to achieve or predict the specified strength properties at early ages,6-8 which includes warm-water curing, autogenous curing, and steam curing.1,9 In recent years, ET curing has been also applied to achieve higher early-age durability properties.5,10 Despite its advantage in obtaining higher early-age strength, ET curing can reduce the long-term compressive strength and durability properties for concrete with only ordinary portland cement (OPC).8,10-12 This reduction in long-term compressive strength has been known as the "crossover" effect.13 In contrast to concrete with...