Evaluation of fly ash reactivity potential using a lime consumption test

Abstract

The reactivity of fly ash, for use in concrete, is normally evaluated in the UK/EU with the Activity Index test (on mortars at 28 and 90 days (BS EN 450-1)). The paper reports on the application of a lime consumption test, based on BS EN 196-5 (pozzolanic cement test), to determine this more rapidly. The method uses a Portland cement (PC) / fly ash slurry, stored for 8 or 15 days at 40°C, and measures OHand CaO concentrations of the filtrate. Seven fly ashes, including those produced using modern power station techniques (e.g. co-combustion, low NOx) and 3 PCs with different characteristics were tested. Early experiments established good repeatability for the test and that pozzolanic reactions mainly occur during the initial 8 to 15 days' storage. Similar behaviour for fly ash was noted to that in thermogravimetric analysis and Activity Index tests from related studies. Strong correlations were obtained for fly ash fineness and CaO consumed. While there was general agreement for CaO consumed and Activity Index, correlations were poor. Similar type effects occur for mortar (Activity Index) and concrete. The lime consumption test can assess fly ash reactivity, but should be combined with measurements of the materials' fineness. 1.

Supplementary cementitious materials: New sources, characterization, and performance insights

“…Unfortunately, most of the existing test methods are found to fall short on one or more of the test method requirements, in particular regarding the range of SCMs covered and correlation to performance. In case of methods that mea C OH 2 as a proxy for SCM reactivity, such as the Chapelle or the Frattini tests, correlation to the compressive strength development of benchmark mortar bars is not clearly apparent and cannot be extended to cover both pozzolanic and latent hydraulic materials [11,124,125]. In addition, a common weakness is the robustness of test methods due to deficiencies in protocol descriptions or reagent specifications [126].…”

Pozzolanic potential of sustainable precursors for engineered geopolymer composites (EGC)

“…Conversely, the SLT [19][20][21] utilizes a fixed amount of Ca(OH) 2 in the solution. It involves adding 1 g of pozzolan to a plastic bottle with 75 ml of saturated lime solution.…”

Influence of wet storage on fly ash reactivity and processing for use in concrete

“…These enabled wet fly ash storage period to be considered and investigation of material moistened and kept under field conditions. Lime consumption experiments, following BS EN 196-5 (BSI, 2011a), used to assess pozzolanic cements and with potential for evaluating fly ash reactivity (McCarthy et al, 2017), and activity index (mortar) tests, as described in BS EN 450-1 (BSI, 2012), were carried out. Measurements of compressive (cube) strength on structural (strength class) concretes were also made.…”

“…Lime consumption (CaO consumed) was measured, based on BS EN 196-5 (BSI, 2011a), sometimes referred to as the Frattini test, following McCarthy et al, (2017). Samples comprising 15•0 g of PC and 5•0 g of fly ash (i.e.…”