A detailed laboratory investigation on evolving the mix design of roller compacted concrete containing RAP aggregates and SCMs

Roller compacted concrete (RCC) is a zero-slump concrete designed for dams and low traffic pavements like parking lots, yards, storage areas etc. The constituents of RCC are similar to conventional concrete but aggregate content is higher, about 10% by volume. Due to the scarcity of natural aggregates, recycled asphalt pavement aggregates (RAP) are used to replace partially or fully the natural aggregates. Literature suggests that RAP inclusion in concrete leads to reduced mechanical properties due to weak interfacial transition zone (ITZ) but also hints about using measures like supplementary cementitious materials to improve these properties. Most of the studies follow one or the other aggregate gradation and aggregate size which definitely alters the properties from one study to the other. So, in this study, a mix design methodology was developed for roller compacted concrete (RCC) by altering the mix design composition of pavement quality concrete (PQC) conforming to IRC: 44, followed by natural aggregate substitution with 50% RAP aggregates by volume, and addition of fly ash (30%) and silica fume (15%) to improve the interphase of paste-aggregate For suitability of the developed mix proportions for pavement applications, its mechanical properties, abrasion and durability were evaluated. Results showed that addition of RAP reduced the compressive and flexural strength in RCC mixes by 24% and 14%, in comparison to the control RCC due to inferior bonding between asphalt coated RAP aggregates and cement paste. Addition of silica fume improved the compressive and flexural strength of RCC–RAP mix values by 9% (32.8 MPa) and 5.5% (3.9 MPa) but the strength values still remain poorer than control RCC. Durability on the other hand improves with the addition of RAP aggregates and it improves further with the addition of SCMs. Porosity and sorptivity decreased by 5.5% and 36.11% respectively, whereas water absorption increased by 3.36% by incorporation of 50% RAP in RCC. Subsequent SCMs addition to RAP–RCC decreased the porosity, sorptivity and water absorption by 28.92%, 55.55% and 20.5%, respectively with respect to control RCC. Considering a minor decrease in strength (< 10%) and a high improvement in durability and abrasion resistance, it is recommended that such concrete pavements can be used for rural roads. In addition, this article proves that RCC could yield a better correlation between destructive and non-destructive tests, and thus is reliable for casting at site.