Silica fume

About: Silica fume is a research topic. Over the lifetime, 10177 publications have been published within this topic receiving 173857 citations.

Non-steady-state accelerated chloride penetration resistance of structural lightweight aggregate concrete

Abstract: This study aims to characterise the chloride penetration resistance of structural lightweight aggregate concrete (LWAC) produced with different types, volumes and initial wetting conditions of lightweight aggregates (LWA), types of cement and contents of fly ash and silica fume, w/c ratios and curing conditions. A comprehensive experimental study was carried out involving three types of non-steady-state tests, which simulate different exposure conditions and penetration mechanisms. It is shown that the chloride penetration resistance is mainly affected by the cementitious paste and that high performance LWAC of 30–70 MPa can be produced. Regardless of the type of aggregate, we propose exponential relations to estimate the diffusion coefficient of chlorides. The volume and initial wetting condition of LWA had little influence on the chloride resistance. A long-term higher reduction of the diffusion coefficient was found in less dense LWAC. Reasonable correlations between the non-steady-state tests were obtained. Contrary to what is suggested in some European standards, the concrete strength cannot properly predict the durability behaviour of LWAC.

Use of the accelerated mortar bar test for evaluating the efficacy of mineral admixtures for controlling expansion due to alkali-silica reaction

Abstract: This paper presents data from laboratory studies to assess the suitability of the accelerated mortar bar test (CSA A23.2-25A and ASTM C 1260) as a method for evaluating the effect of mineral admixtures on expansion due to alkali-silica reaction (ASR). A wide range of materials such as fly ash, slag, silica fume and natural pozzolans have been tested at different replacement levels in combination with various reactive aggregates including siliceous limestone, greywacke, granite and sandstone. Results are presented for 70 different material combinations tested by both the accelerated test and the Canadian Standards Association concrete prism test (CSA A23.2-14A and ASTM C 1293). For aggregates that were shown to be deleteriously reactive by both test methods there was a generally good agreement between the test results when the failure criteria used were expansion of mortar bars at 14 days > 0.10% and expansion of concrete prisms at 2 years > 0.040%. Only 5 out of 70 mixtures passed the mortar bar test and failed the concrete prism test and in two these 5 cases the extent of failure was insignificant (that is, 0.042% expansion at 2 years in both cases). It is concluded that combinations of pozzolans and reactive aggregates that pass the accelerated mortar bar test can be used in the field with a very low (and acceptable) risk of deleterious expansion due to ASR. A large number of the mortar bars were subjected to pore solution expression and analysis after 14 days in 1 M NaOH at 80°C. There is a broad correlation between the pore solution alkalinity and expansion at the end of the test. This suggests that the mineral admixtures suppress expansion in this test by reducing both the alkalinity of the pore solution in the bar and the penetration (diffusion) of alkalis into the bar from the host solution.