Inconsistencies in the pozzolanic strength activity index (SAI) for silica fume according to EN and ASTM

Abstract

New supplementary cementitious materials claimed to possess pozzolan properties emerge frequently. This development is driven both by economic and environmental pressures. Properties of new materials are compared with those of materials already well known, such as silica fume. Several test methods are standardized for making such comparisons, regulated by both European (EN) and American (ASTM) standards. Standardization indicates that procedures are secured to make comparisons valid and informative. In this article the sensitivity of accepted variations within each of the standard procedures are investigated to determine if the results are influenced by such variations. Various methods for testing pozzolanic properties are briefly discussed. Experimental work was carried out in compliance with the standard methods for testing silica fume, according to both EN and ASTM. Seventy two mixes are made and tested in the experimental series, combining two standard procedures, two types of sand, three cements and four flow agents (SP). The results show that determined values are highly influenced by variations accepted to be made within the standard procedures. Possible reasons for these variations are analyzed. Conclusions are made that even when complying with the standards, the results are heavily manipulable (intended or unintended). Also a shortcoming in EN regarding new materials, is detected. Suggestions are made on additional information required to be given together with the results when reporting pozzolanic properties according to standards in order to make results informative and reproducible. A limitation in EN towards testing nano-sized silica materials is detected. An adjustment is suggested, to make EN applicable correspondingly to ASTM, also for these materials.

Enhancement of Material Properties of Lime-Activated Slag Mortar from Intensified Pozzolanic Reaction and Pore Filling Effect

“…The slag is mainly (84.5 wt %) composed of silica (SiO 2 ), alumina (Al 2 O 3 ), and calcium oxide (CaO) components, while the HL is composed mainly (74.5 wt %) of CaO components, induced from Ca(OH) 2 and calcium carbonate (CaCO 3 ). SF has a bulk density of 200-350 kg/m 3 based on the manufacturer's material data sheet, and specific surface area of 15-30 m 2 /g based on the previous measurements [29]; it contains mainly silica (97 wt %), as shown in Table 1. In addition, Figure 1 shows the irregular shaped GGBFS particles, the plate-shaped Ca(OH) 2 in HL particles, and the perfectly globular SF particles.…”

Overview of clay as supplementary cementitious material

“…The CaCO 3 content in raw materials used for Ordinary Portland cement production is about 75 to 79 % [4], making partial replacement of clinker with supplementary cementitious materials (SCMs) a promising option for a more ecological production of concrete. Certain industrial by-products show encouraging results in the clinker substitution [5][6][7]. Fly ash from coal power plants and steel furnace slags have been broadly used as SCMs, but the reserves of these materials are not sufficient to satisfy the cement production demand.…”

Efficiency Concepts and Models that Evaluates the Strength of Concretes Containing Different Supplementary Cementitious Materials

“…They concluded that the efficiency factor for SF concrete with all replacement levels is greater than 1 at 7 days. Recently Thorstensen and Fidjestol,(2015) studied the inconsistencies in the pozzolanic Strength Activity Index (SAI) for SF according to EN and ASTM [44].…”