Investigation of the Effect of Replacing Silica Sand with Sahand Pumice in Reactive Powder Concrete Containing 100% Diatomite Powder instead of Silica Fume

Reactive Powder Concrete (RPC) represents a significant advancement in concrete technology, characterized by its remarkably high compressive strength compared to conventional concrete. This superior performance is attributed to its fine-grained composition, which not only enhances compressive strength but also improves other critical properties such as abrasion resistance, durability, impermeability, and resistance to corrosion. These attributes make Reactive Powder Concrete an ideal choice for various demanding applications in the construction industry, especially in high-performance structures where durability and strength are paramount. This study focuses on an innovative approach to Reactive Powder Concrete production by replacing silica sand with Sahand pumice. The primary objectives of this research include optimizing the use of locally available materials, increasing production capacity, and reducing overall costs. By utilizing pumice, a lightweight volcanic material, the study aims to address challenges associated with sourcing silica sand while maintaining the high-performance characteristics of Reactive Powder Concrete. In this study, a reference mix design for Reactive Powder Concrete was developed, in which diatomite powder was used as a complete replacement for silica fume. This reference mix served as a basis for evaluating the impact of pumice replacement. Subsequently, silica sand in the Reactive Powder Concrete mixtures was replaced with Sahand pumice at varying percentages of 15, 30, 45, 60, 75, 90, and 100 %. All specimens were subjected to water curing at a controlled temperature of 25°C for a period of 28 days. In the conducted experiments, autoclave curing was not used to ensure that the curing conditions resembled normal on-site concreting conditions, making the obtained results more practical and applicable. The study examined several key properties of the concrete, including compressive strength, tensile strength, water absorption during curing and water absorption as per ASTM 1585. Additionally, the flow table test was conducted to determine the consistency of the concrete at each stage before pouring it into the molds. The results showed that as the percentage of pumice replacement increased, the compressive strength of the samples gradually decreased. However, all samples maintained a compressive strength above 50 MPa at 28 days, classifying them as high-strength concrete. For instance, the 28-day compressive strength of the reference Reactive Powder Concrete was recorded at 64.7 MPa. However, at full (100 %) replacement of silica sand with pumice, the compressive strength dropped to 50.7 MPa.  However, it should be noted that this decrease in strength is not necessarily prohibitive depending on the intended application of the concrete. On the other hand, the specific weight of pumice is lower than that of silica sand. Therefore, the use of pumice had a notable effect on the density of the concrete. with increasing replacement percentages, the specific weight of the samples decreased, reaching 1764 g/L at 100 percentage replacement, classifying it as structural lightweight concrete. Despite the reduction in compressive strength, the resulting concrete still qualified as both high-strength and structural lightweight concrete. These classifications were determined based on the standards set forth in the 2017 edition of the National Building Code of Iran. Additionaly, the benefits of using pumice, such as cost savings and enhanced sustainability through the utilization of local materials, offer compelling advantages for specific construction scenarios.