1. Introduction
The utilization of glass products inevitably results in a significant quantity of waste glass, leading to both land resource occupation and substantial environmental pollution [
1]. Nevertheless, recycling glass conserves raw materials, saves energy, and reduces greenhouse gas emissions, thus significantly alleviating environmental pollution and promoting the sustainable use of resources [
2]. However, waste glass contains large amounts of harmful heavy metals such as iron, zinc, and copper and cannot be directly incinerated, landfilled, or treated and decomposed through physical and chemical methods [
3]. Conversely, using glass powder as an admixture in the construction industry provides an effective solution to the issues of waste glass recycling and environmental protection.
In recent decades, scholars, both domestically and abroad, have primarily studied the application of glass as an aggregate and additive gel material in concrete. When waste glass powder is used as a fine aggregate, the quantity mixed in significantly affects the performance of concrete. If the glass powder substitution rate is below 30%, it aids in filling gaps and improving the compactness of concrete, thereby enhancing its mechanical properties and durability. Conversely, a substitution rate exceeding 30% tends to decrease the overall performance of the concrete [
4]. Glass powder can inhibit alkali-silicate reactions when replacing fine aggregate or serving as an auxiliary cementitious material, with the inhibition effect becoming more apparent as the particle size of the glass powder decreases [
5,
6,
7,
8,
9,
10]. When waste glass powder is used as an additive gel material, the concrete’s mechanical properties tend to increase and then decrease with the increase in the glass powder substitution rate, reaching optimal compressive and flexural strengths at a 20% substitution of cement [
11,
12,
13]. Previous studies have shown that glass powder exhibits pozzolanic activity. Initially, this activity is not strong, and the glass powder primarily serves to fill system pores. However, as time progresses, the activity of the glass powder gradually enhances. The glass powder then reacts with calcium hydroxide, a hydration product within the cementitious sand, to generate dense hydrated calcium silicate. This process takes full advantage of the pozzolanic activity of smaller-particle-size glass powder, improving the weak zone of the interfacial transition zone and further enhancing the overall strength of the cementitious sand [
14,
15,
16,
17,
18]. Despite these findings, most studies focusing on the sulfate erosion resistance performance of waste glass powder cement mortar have predominantly focused on equal mass admixture and large particle sizes of glass powder. Research regarding the effects of equal volume admixture and small-particle-size glass powder on concrete durability remains limited, especially in environments subject to salinization, such as coastal areas and Northwestern China. In these settings, research into the resistance of cementitious sand to sulfate erosion becomes increasingly critical.
Substituting a portion of cement with glass powder can enhance resistance to sulfate erosion. Matos et al. [
19] found that the strength-activity indices of glass-powdered cement mortar specimens subjected to alkali-silicate reaction, sulfate attack, chloride penetration, and carbonation in the presence of concentrated sodium sulfate and alkali solutions significantly increased from 28 to 90 days when some of the cement was replaced with glass powder, implying the occurrence of pozzolanic activity. When the cement was mixed with glass powder or silica fume, the non-sulfate-resistant silicate cement used became sulfate-resistant, and the cementitious sand containing glass powder demonstrated increased resistance to chloride penetration. Siad et al. [
20] indicated that the glass powder replacement of cement enhances the sulfate erosion resistance of cementitious materials, primarily due to the low chloride permeability of glass powder concrete and the potential of silica/aluminum-rich residue produced by the pozzolanic reaction of glass powder to inhibit the acidic ionic barrier. Tang et al. [
21] studied the sulfate erosion resistance of sustainable concrete mixed with various solid wastes such as glass powder and fly ash. The results showed that regardless of the dosage, replacing cement with glass powder positively affects sulfate erosion, with the optimum dosage at 20%. Jain et al. [
22] investigated the long-term sulfate erosion resistance effect of glass-powdered concrete with different admixtures. The results showed that when the admixture of glass powder is less than 20%, it positively affects sulfate resistance durability. An X-ray diffraction test was used to evaluate the pozzolanic effect of glass powders. When the dosage exceeds 20%, it negatively impacts the pozzolanic effect, primarily evidenced by the reduced calcium hydroxide crystals. Xu et al. [
23] studied the synergistic effect of using glass powder and a sodium sulfate solution to evaluate the effect of waste glass powder in an alkaline solution. They found that the compressive strength of their 28-day specimens increased by 67% when the sodium sulfate content was 2.5% and the glass powder dosing was 10%. Rashidian-Dezfouli et al. [
24] investigated the effect of three different matrixes consisting of fly ash, glass fibers, and glass powder in a sodium sulfate solution and analyzed the microstructural changes of geopolymers using SEM-EDX and XRD. Their results showed that glass powder-based polymers performed significantly lower than glass fiber and fly ash-based polymers in sodium sulfate solution, which may be related to less stable geopolymerization products that increase porosity and the presence of a large amount of available alkali in the raw glass powder.
In addition to substituting supplementary cementitious materials with glass powder, glass powder further positively impacts sulfate resistance when utilized as an aggregate. Luet et al. [
25] demonstrated that in relation to drying shrinkage, the introduction of glass powder significantly reduces the drying shrinkage of glass-powdered concrete, regardless of the fineness of the glass powder particles. Simultaneously replacing aggregates and additive cementitious materials with glass powder can effectively enhance the resistance of glass powder concrete to sulfate attack. This effect becomes more pronounced with the increased fineness of the glass powder. Shalan et al. [
26] investigated the long-term sulfate resistance of different glass powder mixtures as substitutes for fine aggregates in concrete. The selected fine aggregate was mixed with 50%, 60%, and 100% waste glass powders, and the volcanic ash activity of the glass powder was evaluated using an X-ray diffraction test, which revealed the degree of reduction in calcium hydroxide. The findings indicated that the sulfate resistance of the specimens gradually decreased with the increase in the glass powder admixture. However, concrete mixtures containing 50% glass powder aggregate displayed enhanced sulfate resistance, which was comparable to that of natural aggregates.
Accordingly, previous studies have primarily utilized a specific range of glass powder particle sizes and doses to replace portions of the cement or aggregate in the preparation of cementitious sand and concrete. Nevertheless, determining the optimal dosage of glass powder to replace standard sand, such that the resulting glass powder cementitious sand fulfills basic mechanical properties and durability requirements, has not been widely agreed upon. Likewise, experimental research and theoretical analysis regarding the use of glass powder as a fine aggregate in sulfate solutions are insufficient. This study investigates the effect of glass powder dosage, particle size, and erosion age on the durability properties of glass-powdered cementitious sand when glass powder is substituted for fine aggregate. Moreover, it performs mass loss rate, flexural strength, and compressive strength tests on glass powder cementitious sand specimens to comprehensively analyze glass powder cementitious sand.
4. Conclusions
The erosion of cementitious sand by sulfate is a multifaceted process, subject to numerous factors. This paper delves into the role of 100–200 mesh and 200–500 mesh glass powder in mitigating sulfate erosion when used to replace standard sand with cementitious sand. The primary conclusions are as follows:
(1) The erosion damage of cementitious sand initiates from the surface and progresses inward. Initially, sulfate ions act on the specimen’s surface, with pronounced erosion effects at the corners. As the surface erodes and begins to degrade, micro-cracks form on the specimen’s surface. This enables sulfate ions to reach the internal, cracked areas and react with Ca(OH)2 to generate expansive materials, such as gypsum and calcium alumina. This causes erosion products to deposit within the cracks and pore spaces. As more sulfate ions penetrate the specimen, the production of these expansive materials increases within the specimen, which subsequently reduces its original mechanical properties until complete disintegration occurs.
(2) With the addition of 15% 100–200 mesh glass powder, flexural and compressive strengths decrease significantly between 30 to 60 days of the initial erosion. However, the decrease in flexural strength from 90 to 150 days slows down by only 1% in tap water and 13.9% in sodium sulfate solution. In contrast, compressive strength rapidly increases by 79% in tap water and 44.5% in sodium sulfate solution. With the addition of 10% and 15% 200–500 mesh glass powder, the flexural strength declination slows, and the compressive strength declination becomes quicker in the early erosion stage of 30 to 60 days, whereas in the later erosion stage of 90 to 150 days, the flexural strength declination accelerates while the compressive strength increases.
(3) When increasing the quantity of the same-particle-size glass powder, the flexural and compressive strengths of glass powder cement sand in tap water and sodium sulfate solution decrease. The optimal anti-sulfate erosion performance is observed in specimens of cement sand mixed with 10% 200–500 mesh glass powder. This is primarily because an excessive concentration of fine glass powder enlarges the specific surface area of the glass powder, causing an increase in moisture absorption and slurry consistency. Consequently, the water available for cement hydration is reduced, which affects the content of CH, the hydration product of cement, and ultimately inhibits the full activation of the glass powder, resulting in a slight decrease in strength.
(4) As particle size decreases, the mass loss rate’s decreasing trend noticeably slows while flexural and compressive strengths gradually enhance, indicating a progressive enhancement in sulfate erosion resistance. This is primarily because finer glass powder has a stronger pozzolanic effect, producing densely hydrated calcium silicate crystals. Additionally, finer glass powder has a stronger micro-aggregate filling effect, which reduces the internal pore structure of the mortar and compensates for the lower strength of the interfacial transition zone, thereby preventing sulfate ions from infiltrating the test specimen’s interior, leading to expansion, internal cracking, and eventual destruction.