Effect of GU vs. GUL Cement on AAR Testing of Concrete Aggregates

Abstract

Alkali-Aggregate Reaction (AAR) is a severe deterioration affecting concrete infrastructures worldwide. AAR occurs when the aggregates react with the alkalis in cement used for the concrete, thereby producing pressure within the concrete that causes expansion, deterioration and cracking. The Ministry of Transportation (MTO) evaluates the reactivity of concrete aggregates using the MTO laboratory methods, Accelerated Mortar Bar Test (LS-620) and Concrete Prism Test (LS-635), demanding the use of Portland Cement (GU). The introduction of Portland-limestone (GUL) cement calls for an investigation of the aggregate reactivity with GUL cement using the two test methods. The findings would support the ministry’s understanding of the difference in expansion with the use of GU and GUL cements and any impact of using GUL cement on the two test methods.

This paper reports on the LS-620 test data on four MTO reference aggregates (two quarried siliceous limestones (ASR CA3 and CA6) from Ottawa area, a quarried dolomitic limestone (ACR CA1) from Kingston area, and a crushed siliceous gravel (ASR CA5) from Sudbury area) using both GU and GUL cements from cement suppliers in Canada. The data were produced through MTO Aggregate and Soil Proficiency Program and MTO-Toronto Metropolitan University partnering program. Multi-stage statistical methods were used to analyze the data.

The precision estimates calculated for ASR CA6 suggested that for expansion of more than 0.3%, the variations in expansion with GUL cement are comparable to the variations obtained for GU cement from the same supplier. It was also found that the difference in expansion between GU and GUL was comparable to the difference in expansion with GU cement from different suppliers.

In comparing the expansions between the use of GU and GUL cements from the same supplier, ANOVA analysis of ASR CA3 expansion data showed no significant difference, while the analysis of ASR CA6 expansion data showed a significant difference.

A calculation of Percent Within Limits (PWL) using the ASR CA6 expansion data suggested that 94% to 95% of the expansion results using GUL cement will fall within the expansion range obtained by using GU cement from the same supplier. This showed that the significant difference in expansion suggested by ANOVA for ASR CA6 was masked by the current variability of the test method LS-620 and that the use of GUL cement may not have a significant impact on the test method.