Date: Thursday, Feb 2nd
Presenter: Matt Adams and Tengfei Fu, OSU Civil and Construction Engineering
Matt Adams abstract:
Alkali-Silica Reactivity of Recycled Concrete Aggregates
The use of recycled concrete aggregate (RCA) in concrete is a promising method to decrease the amount of demolished concrete sent to landfills. Replacing natural aggregate (NA) with RCA in new concrete is severely hindered, however, by a lack of technical information on the long-term durability of this concrete. This research focused on assessing the reactivity of alkali-silica reaction (ASR) affected RCA when incorporated into new concrete using current testing methods; and the efficacy of replacing portland cement with supplementary cementitious materials (SCM), known to mitigate alkali-silica reaction (ASR) in concrete with virgin aggregates, to control ASR in concrete incorporating reactive RCA. Eight different recycled concrete aggregates were investigated as a part of a multi-laboratory study that involved four universities. The supplementary cementitious materials investigated include: fly ash, silica fume, and metakaolin. The results of alkali-silica reactivity tests, ASTM C 1260 and ASTM C 1567, will be presented for the recycled concrete aggregates when using 100% portland cement, binary blends of portland cement and fly ash, and ternary blends of portland cement, fly ash and other SCMs. These test methods wereeffective in detecting aggregate reactivity but expansion varied depending on the processing, age, and mineralogy of the RCA. The results have also shown that, when compared to SCM amounts required to reduce expansion in NA concrete, up to a 25% increase in the amount of SCMs needed to control ASR is required for concrete containing 100% RCA made from parent concrete containing that same NA.
Tengfei Fu abstract:
Long-Term Chemical Shrinkage for Blended Portland Cement
In the past ten years, renewed research interest has shown the benefits of internal curing by incorporating pre-wetted lightweight fine aggregate (LWFA) in high performance concrete (HPC). To determine the optimum LWFA content, information about the propensity for shrinkage in the cement paste, specifically the chemical shrinkage value, is needed. However, there is a lack of information on how to determine the long-term chemical shrinkage value for HPC with supplementary cementitious materials (blended systems) and/or shrinkage reducing admixture (SRA). The purpose of this research was to identify a simple procedure to determine long-term chemical shrinkage values for given cementitious systems with SCMs and/or SRA. Several improvement to the ASTM C1608 (dilatometry procedure) were investigated. An experimental prediction model was adopted and verified to estimate long-term chemical shrinkage values for portland cement systems containing SCMs and/or SRA. A recommended procedure is proposed to determine the long-term chemical shrinkage values for HPC systems containing SCMs and/or SRA, and a modification to a commonly used LWFA proportioning equation is suggested.
Tengfei Fu is a PhD candidate who is investigating drying shrinkage limits of high performance concrete for Oregon DOT. He completed his M.S. in February or 2011 with a focus on early-age properties of high performance portland cement concrete and calcium aluminate cement concrete. He is a recipient of PCA Education Foundation Research Fellowship in 2011.