# Performances of the Synergy of Silica Fume and Waste Glass Powder in Ternary Blended Concrete
## 1 Introduction  
The world annual increase in cement production is to the tune of 2.5% with the gross production of about 4.6 billion tonnes. This has called for the exploration of alternative materials for the partial substitution and management of the proliferation of carbon dioxide into the atmosphere [1]. In several countries around the globe, the use of up to 60% supplementary cementitious materials for the sake of the economy and durability performance has been established. According to the Glass Packaging Institute (GPI), the recyclable glass content was about 3.1 million tons at an increase rate of 31.3%, while combusted glass was estimated to be 1.6 million tons. The glass in landfills was about 5.2% (7.6 million tons) of the total glass in municipal solid waste [2]. Previous studies have shown that the use of waste glass powder (WGP) as an active addition to concrete provides economic and environmental benefits [3], even if it is incorporated as a fine aggregate in white cement mortars [4]. Glass has been used as a supplementary cementitious material in several other studies [5, 6, 7], but in the majority of them it was recommended that 10-20 wt.% WGP can be utilized as a cement replacementwith a continuous decrease in compressive strength [8] reported that mortars with ground glass immersed in water for seven years have not shown signs of deterioration and have higher compressive strength. Even though glass has high alkali content, [9] asserted that it released only a very small fraction of sodium into the pore solution, thereby making it a safer additive. [PERSON] et al. [10] reported the results of three concrete mixes comprising OPC, fly ash and silica fume. In all three mixes, the cement content was replaced by 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% of waste glass powder. The results of the tests showed that WGP up to 5 wt.% can partially replace OPC in concrete that exhibits better tensile and compressive strengths than fly-ash- and silica-fume-based concrete. Additionally, a higher replacement of up to 20 wt.% WGP could reduce the tensile and compressive strengths by 13% to 14%, respectively. Despite the aforementioned, there are some disadvantages associated with utilizing glass in concrete such as a low early strength that could pose a challenge, especially where the early stripping of formwork is required in construction practice [11]. Silica fume, being a by-product of silicon and ferrosilicon alloy and environmental solid waste that contains about 75% silica [12], has the capability to contribute to the strength, as well as reduce the permeability and bleeding of concrete due to its pozzolanic effects [13]. It, however, has some setbacks, such as lowering the workability [14; 15], and setting time of the concrete mixture [16] when the correct proportion is not used. The quantity of silica fume for an effective performance is reported to be in the range of 10-15 wt.% [17; 18]. Waste glass powder (WGP), however, can contribute to the consistency of concrete mixture [19], due to its glassy surface with low water absorption. Both glass waste and silica fume up to 10-25 wt.% have been independently reported to contribute to compressive strength after a period exceeding 90 days [5]. Ref. [20] compared glass compositions with an observable increase in workability (flowability) and a decrease in setting time. A similar finding was reported by [21], while [22] reported a decrease in structural networks build up from 7.1 to 0.8 Pa/min with an increase in viscosity from 0.118 to 0.013 Pa/se. Another benefit of the use of glass waste was also derived from the use of cullet glass waste as a substitute for natural sand during the synthesis of an alkaline binder by using ground granulated blast furnace slag and fly ash as precursors. Positive results of durability performance were also reported for sand replacement by glass waste at the level of 25-100 wt.% within the temperature range of 200-800 \({}^{\circ}\)C [23; 24].