# Internal Curing Effect of Waste Glass Beads on High-Strength Cement Composites
###### Abstract  
High-strength concrete (HSC) uses binders and microfillers with ultrafine particles, such as silica fume. The resulting dense internal hydration structure rapidly decreases HSC humidity, causing shrinkage cracks and affecting internal hydration. Herein, the hydration degree inside high-strength cement composites (HSCs) was examined using waste glass beads (WGBs) as lightweight aggregates (LWAs). Moreover, unreacted hydrate reduction and hydrate formation tendencies were investigated. WGBs with particle sizes within 2.00-6.00 mm were added at ratios of 5%, 10%, and 20% after pre-wetting. The increased number of hydrates inside the specimens were examined under steam curing (80 \({}^{\circ}\)C) and room temperature curing (25 \({}^{\circ}\)C). The strength decreased as the WGB content increased. Thermogravimetric, X-ray diffraction, and Si nuclear magnetic resonance analyses revealed that the hydration degree of Si inside HSCs changed when the content of pre-wetted LWAs changed. A visual inspection of the specimen cross-section and scanning electron microscopy-energy-dispersive X-ray spectrometry (SEM-EDS) analysis revealed the moisture trapped inside WGB pores and the hydration tendency. Under steam curing and room temperature curing, the paste contained different amounts of hydrates, depending on WGB content. Moreover, water-absorbed WGBs were continuously desorbed through SEM-EDS, and hydrates were present in WGB pores. high-strength cement composites; densification; waste glass bead; Si hydration; correlation analysis 202220202202202202202022020220202022020220202202020220202022020220202202022020202202022020220202202022020220202202022022020220220220202202202202022020  
internal curing technique for concrete using porous lightweight aggregates (LWAs) has various benefits, such as reducing shrinkage and cost [5]. In a related study, [PERSON] et al. increased the degree of hydration using a method similar to increasing the water-to-cement ratio inside the matrix by a hydration process using superabsorbent polymers (SAPs) and investigated the resultant internal hardening [6]. [PERSON] et al. and [PERSON] et al. verified the mechanism through which SAP absorbs and releases moisture inside concrete [7; 8; 9]. [PERSON] et al. applied the moisture absorption property of rice husk ash to UHPC and confirmed its effect on improving strength [10]. [PERSON] et al. applied porous aggregates comprising calcined bauxite and basalt aggregates to UHPC and proposed a method to improve matrix strength, excluding fibers [11]. [PERSON] et al. investigated the effect of moisture transport of porous aggregates on the shrinkage reduction and microstructure optimization of UHPC and reported a method for designing a UHPC matrix using a high-density particle packing model (Andreasen and Andersen model) [12]. To study hydration inside UHPC with LWA for strength improvement, the hydrates generated inside specimens were detected using thermogravimetric analysis (TGA) and scanning electron microscopy-energy-dispersive X-ray spectrometry (SEM-EDS). Based on the aforementioned results, many studies have improved the hydration degree inside UHPC using porous materials. Most of the internal curing materials currently used in UHPC are porous. The addition of SAPs and LWAs is the most commonly used method because these materials can significantly inhibit the increase in the autogenous shrinkage of UHPC and fully compensate for the initial shrinkage of concrete [13; 14; 15]. However, SAPs and LWAs contain numerous pores, which may degrade the mechanical properties and durability of UHPC by increasing the number of pores. Therefore, pre-wetted LWAs can effectively minimize the extent of drying and autogenous shrinkage of UHPC [16]. [PERSON] et al. reported that the moisture introduced into concrete by LWA can inhibit internal shrinkage and cracking as well as improve the hydration degree of the surrounding mortar, thereby improving the strength of concrete [17; 18; 19]. [PERSON] et al. and [PERSON] et al.