Individual and Combined Effects of Chloride, Sulfate, and Magnesium Ions on Hydrated Portland-Cement Paste

Pub Date : 1994-03-01 DOI:10.2172/10147904

T. Poole, L. D. Wakeley, C. L. Young

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引用次数: 2

Abstract

Ground water with a high concentration of magnesium ion is known to cause deterioration to portland cement concretes. A proposed mechanism for this deterioration process published previously involves an approximate 1:1 replacement of Ca ions by Mg ions in the crystalline phases of hydrated cement. The current study was undertaken to determine which ions, among magnesium, chloride, and sulfate, cause deterioration; whether their deleterious action is individual or interdependent; and to relate this mechanism of deterioration to the outlook for a 100-yr service life of concretes used in mass placements at the Waste Isolation Pilot Plant. Loss of Ca ion by cement pastes was found to be strongly related to the concentration of Mg ion in simulated ground-water solutions in which the paste samples were aged. This was true of both salt- containing and conventional cement pastes. No other ion in the solutions exerted a strong effect on Ca loss. Ca ion left first from calcium hydroxide in the pastes, depleting all calcium hydroxide by 60 days. Some calcium silicate hydrate remained even after 90 days in the solutions with the highest concentration of Mg ion, while the paste samples deteriorated noticeably. The results indicated a mechanism that involves dissolutionmore » of Ca phases and transport of Ca ions to the surface of the sample, followed by formation of Mg-bearing phases at this reaction surface rather than directly by substitution within the microstructure of hydrated cement. Given that calcium hydroxide and calcium silicate hydrate are the principal strength-giving phases of hydrated cement, this mechanism indicates the likelihood of significant loss of integrity of a concrete exposed to Mg-bearing ground water at the WIPP. The rate of deterioration ultimately will depend on Mg-ion concentration, the microstructure materials of the concrete exposed to that groundwater, and the availability of brine.« less

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氯离子、硫酸盐离子和镁离子对水合波特兰水泥浆体的单独和联合影响

众所周知，含有高浓度镁离子的地下水会导致波特兰水泥混凝土的变质。先前发表的一种退化机制涉及水化水泥结晶相中钙离子被镁离子约1:1取代。目前的研究是为了确定镁、氯化物和硫酸盐中哪些离子会导致恶化;他们的有害行为是单独的还是相互依存的;并将这种恶化机制与废物隔离试验工厂大量放置的混凝土的100年使用寿命前景联系起来。水泥浆中钙离子的损失与模拟地下水溶液中镁离子的浓度密切相关，其中水泥浆样品经过老化处理。这对含盐水泥和常规水泥都是如此。溶液中没有其他离子对钙的损失产生强烈的影响。钙离子首先从糊状物中的氢氧化钙中释放出来，在60天内耗尽所有的氢氧化钙。在Mg离子浓度最高的溶液中，部分水合硅酸钙在90天后仍然存在，而膏体样品明显变质。结果表明，这一机制涉及到Ca相的溶解和Ca离子向样品表面的运输，随后在该反应表面形成含镁相，而不是直接通过水化水泥微观结构内的取代。考虑到氢氧化钙和水化硅酸钙是水化水泥的主要强度赋予相，这一机制表明，在WIPP暴露于含镁地下水的混凝土可能会严重丧失完整性。劣化的速度最终取决于镁离子浓度、暴露在地下水中的混凝土的微观结构材料以及盐水的可用性。«少

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