Performance-Based Design Considerations for Abrasion Resistant Concrete for Structures in Mineral Processing Plants

Abstract

Impact and abrasion-wear on reinforced concrete (RC) silos used for ore material storage in mineral processing has over the years resulted in costly deterioration, mining operation downtime, and structural failure in some severe cases. Despite the current advancements in the study of abrasion resistance, and the limited knowledge of tribosimulative abrasion resistance testing, further advancements are needed to allow for the development of performance-based design considerations for concrete structures in abrasive exposure environments. In this research, a structural assessment is conducted on a platinum processing plant RC silo using the Anglo-American guideline to qualify and evaluate the aggressiveness of the exposure environment, and its influence on the silo’s internal wall concrete deterioration. The information obtained from the assessment report, with respect to the design specifications and concrete performance, is then used to advise the research methodology followed in the experimental work. In addition to the results from the laboratory analysis, the information is then contrasted against the findings in literature and used to propose abrasion resistance performance-based criteria for silos in mineral processing. The SANS 1058 abrasion test was identified as the most tribosimulative test for assessing the impact and abrasion wear of silo concrete during loading and unloading operations in mineral processing. This test was then employed to explore the abrasion resistance properties of various concrete mix designs. A total of 324 cubes, with 18 distinct mixes were cast and cured for 3, 7, 28 and 7,14 and 28-days for the concrete compressive strength and abrasion resistance tests respectively. The 18 distinct mixes consisted of a permutation of dolerite, granite, and andesite aggregates with the following aggregate sizes; 13,2 and 19 mm, binder types; 100% PC, 85/15 PC/FA, 92.5/7.5 PC/CSF, and a w/c ratio of 0.4. These mixes were compared against each other to establish the influence of the variation in aggregate type, size, and binder types on the compressive strength and abrasion resistance of concrete. Additionally, an analysis of the workability and setting times of the above-mentioned mixes was conducted to evaluate the salient constructability requirements for the construction of bulk storage silos using the slip-form method, as outlined by the American Concrete Institute (ACI). The results show a considerable influence of concrete compressive strength on the development of abrasion resistance, where the increase in compressive strength resulted in an increase in abrasion resistance. However, minimal improvement in the abrasion resistance was observed when the concrete strength was increased further than 70 MPa, where the average abrasion mass loss observed was less than 1 g for all the mixes, except for the mixes with the granite aggregates, which will be discussed below. At 28 days, the aggregates were observed to have a more pronounced influence on the abrasion resistance performance when compared to the influence of binder type. It was found that the aggregates with lower LA (Los Angeles) Abrasion %, ACV %, and higher aggregate densities resulted in higher abrasion resistance. Dolerite and andesite aggregates had the lowest LA abrasion, ACV%, and higher densities when compared to the granite aggregate mixes. These andesite and dolerite mixes (both 13,2 and 19 mm) were observed to exert a substantial influence on the reduction of abrasion mass loss at a constant w/c ratio, with a 96 and 111 % difference in abrasion mass loss observed between the andesite and granite, and the dolerite and granite mixes respectively. Furthermore, the mixes with the granite aggregates were observed to show the greatest abrasion mass loss observed throughout the 28-day test period, due to the significantly high LA abrasion%, ACV%, and lower aggregate densities when compared to the other aggregate types mentioned above. Lastly, the findings from this study advocate for the application of material storage and flow principles along with advanced concrete technology to mitigate the deterioration of concrete silos due to impact and abrasion wear. Additionally, the results obtained from the study were then used to propose performance-based design acceptance criteria and considerations for impact and abrasion-resistant concrete with respect to the relevant exposure conditions. These are based on allowable mass loss values at 28 days, the constituents of concrete, and the effects of the exposure environment on the above mentioned performance criteria.