Abstract
A freeze-thaw resistance is an important indicator of the durability of alkali-activated slag concrete, which causes structural failure when the performance is low, especially in severely cold areas. In this study, solid sodium aluminate and sodium silicate were used as composite alkaline activators, while slag was used as the raw material to prepare alkali-activated slag concrete, whose freeze-thaw resistance, as well as that of ordinary cement concrete, was experimentally studied by varying the freeze-thaw cycles. The effects of the mass, compressive strength, and dynamic elastic modulus of the sample were investigated by considering the influence of different water-to-slag ratios and slag contents, while the damage variables and model were also analyzed. The results showed that alkali-activated slag concrete had an excellent freeze-thaw resistance, which was significantly affected by the water-to-slag ratio and compressive strength; specifically, the higher the water-to-slag ratio, the lower the freeze-thaw resistance, and the higher the compressive strength, the better the freeze-thaw resistance. The freeze-thaw durability, microstructure, and damage mechanism were studied via microscopic analysis. When analyzed via the microstructure test, crack pores and microcracks with narrow spaces and large surface areas were generated under freeze-thaw damage conditions, but the dense hydration structure and high-bonding-strength hydration products led to a better freeze-thaw resistance. The damage model was established using compressive strength and relative dynamic elastic modulus as damage variables, and the attenuation exponential and accumulative damage power function model had a high accuracy, which could better reflect the freeze-thaw damage law and damage degree and predict the lifetime of alkali-activated slag concrete.
Highlights
Cement and concrete have been widely used in construction and civil engineering for over a century, while the production of cement entails several challenges that are environmentally detrimental, such as intensive carbon dioxide emissions and high energy consumption [1, 2]. ese environmental problems have become more prominent with societal development, and more attention has been paid to alkali-activated slag and alkali-activated slag concrete (AASC) as new green gel materials [3, 4]. e alkali-activated slag gel material consumes less energy and emits less carbon dioxide than cement in terms of production [5,6,7,8]
Krivenko [13] studied the influence of different liquid alkalis activated on the freeze-thaw resistance of AASC and found that AASC with any activated liquid alkali could withstand 300–1300 freeze-thaw cycles, while ordinary cement concrete (OCC) could only withstand less than 300 cycles
E freeze-thaw cycle test was performed using the BC10 freeze-thaw test box, and the transverse fundamental frequency and dynamic elastic modulus were measured using a DT–20 dynamic bomb instrument, while the quality value was measured using an electronic scale with an accuracy of 0.001 kg, which was based on the GB/T 50082 standard [19]. e mass and transverse fundamental frequency of the prism sample was measured every 25th freezethaw cycle, with a cycle target of 300. e quality value is the mean value of the three quality samples in each group. e dynamic elastic modulus and relative dynamic elastic modulus values were the mean values of the three samples in each group
Summary
Cement and concrete have been widely used in construction and civil engineering for over a century, while the production of cement entails several challenges that are environmentally detrimental, such as intensive carbon dioxide emissions and high energy consumption [1, 2]. ese environmental problems have become more prominent with societal development, and more attention has been paid to alkali-activated slag and alkali-activated slag concrete (AASC) as new green gel materials [3, 4]. e alkali-activated slag gel material consumes less energy and emits less carbon dioxide than cement in terms of production [5,6,7,8]. The basic properties of AASC have been widely reported, and some studies have focused on frost resistance [11, 12], while research on the relationship between the microstructure and frost resistance of AASC is lacking, and studies on freeze-thaw damage laws and models are rare. Most of the previous studies used liquid alkaline activators to obtain the best mechanical properties of AASC, but the corrosive damage caused by the alkaline liquid in the preparation and curing process is a problem that needs to be considered. Previous studies used a set of composite solid alkaline activators, which had been confirmed to present better mechanical properties at room temperature curing times but did not achieve the research objectives in terms of durability to reduce the corrosive damage generated during the preparation and curing processes. The importance of the damage theory regarding freeze-thaw damage was considered, and combined with mathematical simulation, AASC freeze-thaw damage models were established, which provided basic data for the prediction of AASC freeze-thaw damage in severely cold regions
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