The use of supplementary cementitious materials (SCM) is projected to increase because they reduce the global warming potential of concrete. When cement is replaced with SCM, the flow of the mixture may change. The porosity of the paste may also change as the liquid-to-solid volumes change when mass replacement is used. This paper discusses the role of water absorption and the specific gravity of the SCM on the water requirements of a mixture. Over thirty SCMs were tested, including sixteen natural pozzolans, ten coal ashes, three blended pozzolans, and one ground glass. The porosity of the SCM was measured using a drying rate test. The water absorbed by the natural pozzolans ranged from 3.25 to 17.25 %, 5.55–9.25 % for blended pozzolans, 4.10–18.95 % for coal ashes, and 4.20 % for ground glass. The water requirement measured using ASTM C311 ranged from −4.25 to 46.2 %. The specific gravity of the SCM is particularly important when it is significantly different from the specific gravity of the OPC, as this can change the liquid-to-solid volume ratio. Accounting for the absorption of water by the SCM and the specific gravity of the SCM (via volume replacement) resulted in 55 % of the specimens having a water demand within ±5 % of the original mixture to achieve the same flow, and 94 % of the samples had a water demand within ±20 %. This was substantially less than mass replacement. Using volume replacement and accounting for SCM absorption would have water requirements more similar to the original mixtures.

中文翻译：

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补充胶凝材料的吸水和比重对所需水的影响


预计辅助胶凝材料 （SCM） 的使用将会增加，因为它们降低了混凝土的全球变暖潜力。当用 SCM 代替水泥时，混合物的流动可能会发生变化。当使用质量置换时，浆料的孔隙率也可能随着液-固体积的变化而变化。本文讨论了 SCM 的吸水率和比重对混合物需水量的影响。测试了 30 多种 SCM，包括 16 种天然火山灰、10 种煤灰、3 种混合火山灰和 1 种磨砂玻璃。使用干燥速率测试测量 SCM 的孔隙率。天然火山灰吸收的水量为 3.25 至 17.25 %，混合火山灰为 5.55-9.25 %，煤灰为 4.10-18.95 %，磨玻璃为 4.20%。使用 ASTM C311 测量的需水量范围为 -4.25 至 46.2 %。当 SCM 的比重与 OPC 的比重明显不同时，SCM 的比重尤为重要，因为这会改变液固体积比。考虑到 SCM 对水的吸收和 SCM 的比重（通过体积置换），导致 55% 的样品需水量在原始混合物的 ±5% 以内，以实现相同的流量，94% 样品的需水量在 ±20% 以内。这大大少于质量替换。使用体积置换并考虑 SCM 吸收量将具有与原始混合物更相似的需水量。