Abstract
At present, not many studies have considered methods to quantitatively evaluate the reaction efficiency of granulated blast furnace slag (GBFS) at different curing temperatures. For high volume slag concrete, when the replacement ratio exceeds a certain ’threshold’ value, the superfluous and ineffective slag will no longer react in concrete but simply behave as a fine aggregate, which may cause the decrement of strength. The ’threshold’ value depends on the reaction efficiency of slag. In this study, experiments on mortars with different replacement ratios by slag were conducted at different curing temperatures (20, 30, and 50 °C, respectively), the threshold values of effective replacement ratio by slag were comprehensively analyzed through the reaction efficiency of slag mortar. The results showed that the turning point of the strength curve with replacement ratio can be considered as the threshold value of the effective replacement ratio by slag in mortar. Along with the curing temperature enhancement, the threshold value of the effective replacement ratio by slag in concrete decreased, whereas the reaction efficiency of slag increased. Meanwhile, the analysis of cement effective coefficient (k value) and basicity was also calculated. Based on the obtained threshold values of effective replacement ratio at different curing temperatures, the formula for the determination of reaction efficiency coefficient of slag in the mortar can be established. Therefore, the reaction efficiency coefficient and upper limit of the effective replacement ratio of slag at different temperatures can be calculated more intuitively and quantitatively, providing a theoretical basis and reference for practical engineering applications.
Highlights
According to the Market Development Research and Investment Prospects Report of Slag PowderIndustry in China, the output of the slag powder industry in 2018 is huge, at 103 million tons [1].due to the development slowdown of infrastructure construction and real estate industry, the overall downturn of the building materials industry has brought about higher requirements for the utilization of slag powder in practical engineering applications, with the use of high content granulated blast furnace slag (GBFS) not allowed in more demanding environments, the proportion of slag powder would be reduced further, and the comprehensive utilization of slag powder is facing serious challenges [2]
Based on GB/T 50081-2002, the specimens with in the shape of Φ50 × 100 mm cylinders were prepared for the tests of compressive strength of different slag mortars, the tests were conducted at the ages of 3, 7, 14, 28, and 91 days, respectively, three identical specimens were tested per age for each specimen design
The following results were obtained in this study: (1) The upper limit of effective replacement ratio of GBFS in high volume slag mortar depends on the reaction efficiency of GBFS at different curing temperatures
Summary
Due to the development slowdown of infrastructure construction and real estate industry, the overall downturn of the building materials industry has brought about higher requirements for the utilization of slag powder in practical engineering applications, with the use of high content granulated blast furnace slag (GBFS) not allowed in more demanding environments, the proportion of slag powder would be reduced further, and the comprehensive utilization of slag powder is facing serious challenges [2]. Ishida T reported that with the increase of the replacement ratio by granulated blast furnace slag (GBFS), the Ca(OH) amount of concrete decreased, and the consumed Ca(OH) amount increased because of the slag hydration. When the replacement ratio was over 67%, the remaining Ca(OH) amount was close to 0 [3]. It may be known, when the replacement ratio exceeds a certain
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