喀腊塑克水库混凝土集料碱活性试验研究

用岩相法、砂浆棒快速法、砂浆长度法等多种方法对喀腊塑克水库工程所用集料的碱活性进行研究.试验结果表明.料场集料中含有属于低活性或反应缓慢的碱活性集料.为确保工程安全,应采取工程措施抑制碱一集料反应.     

高温、高压、高碱下的碱一集料反应

快速鉴定集料的碱活性是当前世界各国科学家一致追求的目标。本文详细介绍我们所提出的快速法的各种试验条件选择的依据。通过加温、加压、加碱等强化碱—集料反应条件的试验与显微观察,论证了利用测长法研究、鉴定碱—集料反应时,提高试体养护温度和压力是可能的。对硅酸型活性集料最佳试验温度为150℃,此外还要控制在一定时间内。同时还介绍了水泥中碱含量,浸泡液碱浓度、水灰比、试体预养条件、集料粒径、水泥与集料之比等对膨胀率的影响。在上述各种试验条件的基础上,根据研究、鉴定碱—集料反应试验要求,通过选择适宜的试验条件研究碱—集料反应。证明选择适宜的强化条件进行试验不但效果好,还可大大加快反应速度,得到一些短期内难以得到的规律。     

碳酸盐反应活性的新快速鉴定方法

系统研究了大量具有不同化学组成、结构和地质特征的碳酸盐集料 ,并选择加拿大Kingston的碱活性碳酸盐集料作为标准进行对比试验。研究内容涉及集料的化学组成、矿物分析和岩相检验 ,集料不同颗粒大小的碱碳酸盐反应动力学 ,探讨并否定了 80℃下晶体热致膨胀因素的影响。根据试验结果提出了一种新的评价碳酸盐集料碱活性的方法。方法的主要试验参数为 :集料尺寸 5～ 10mm、水泥中碱质量分数 1.5 0 % (等当量Na2 O)、水灰比0 .3的小混凝土试件在 80℃、1mol/L的NaOH养护溶液中养护 14d的试件膨胀率大于 0 .10 %。     

硅粉抑制碱集料反应的试验研究

通过对青海地区的集料调研分析,发现青海大部分地区的集料存在高的碱活性.采用西宁城北地区典型的砂石集料以及大通地区的集料进行了试验研究,对比分析了不同掺量的硅粉对碱集料反应的抑制效果.结果表明:对于城北石、大通石两种碱活性较低的集料,选择掺量10％、15％、20％硅粉时,其14d膨胀率均小于0.1％,均能有效抑制碱集料反应的膨胀.而对于城北砂碱活性较高的集料,选择掺量20％硅粉时,其14d膨胀率小于0.1％,可以有效抑制碱集料反应的膨胀.     

硅质集料碱活性快速砂浆棒试验方法3.砂浆试件尺寸的影响与试验龄期的确定

研究了砂浆试件尺寸与碱 -集料反应试件膨胀的关系。结果表明尺寸对试件膨胀的影响很小。与 2 cm× 2cm× 8cm试件相比 ,使用 4cm× 4cm× 1 6cm试件 ,试验准确性更高。用本文研究的新方法、CECS48∶ 93和ASTM C1 2 60等方法对比试验花岗岩砂、砾石砂和卵石砂等集料碱活性 ,确定新方法的试验龄期为 5d和 1 4d。     

LiOH抑制碱-硅酸反应膨胀及其应用研究

研究了沸石化珍珠岩混凝土在KOH,LiOH溶液中压蒸膨胀行为,通过扫描电镜和能量散射谱对产物的形貌和组成进行了分析,说明LiOH抑制碱-硅酸反应膨胀的机理主要是在集料周围形成了含锂盐的非膨胀性产物,含锂产物层的形成对活性集料起保护作用而阻止了碱的进一步侵蚀。研究了由碱-硅酸活性集料和碱-碳酸盐活性集料制成的混凝土在各种碱中的膨胀行为。结果表明：混凝土在相同摩尔浓度的碱中压蒸,在NaOH溶液中膨胀最大,在LiOH溶液中膨胀最小。在应用LiOH抑制碱-硅酸反应膨胀促进碱-碳酸盐反应膨胀的双重作用下,在Spratt细粒硅质灰岩中,少量的白云石在碱环境中可发生去白云石化作用而对膨胀有贡献,也即尽管Spratt灰岩中碱-硅酸反应是主要的,但也存在碱-碳酸盐反应。     

RILEM AAR-5与其它快速法对集料ASR活性检测的对比与评价

试验采用RILEM AAR-5小混凝土柱法、ASTM C1260砂浆棒快速法、CECS48压蒸法和RILEM AAR-4加速混凝土棱柱体法检测了石门坎砂岩、两河口砂岩、锦屏砂岩、舟山安山岩和硅质白云岩的碱-硅酸反应活性,并将几种试验方法的结果进行比较,以评价RILEM AAR-5对硅质集料碱-硅酸反应活性检测的适应性.结果表明,对于慢性膨胀集料锦屏砂岩,RILEM AAR-5比ASTM C1260和CECS48检测更准确;硅质集料的小混凝土柱法(RELEMAAR-5)28 d膨胀率可以很好的预测混凝土棱柱体法试验结果;硅质集料尺寸与膨胀率的大致关系为RILEM AAR-5(5～10 mm,28 d)＞ASTM C1260(0.16 ～5 mm,14 d)＞CECS48(0.16 ～0.63 mm,6 h);碱-硅酸反应除受活性组分(化学因素)影响外,活性组分在集料中的分布(构造特征)也有重要作用.     

波茨坦砂岩的微观结构和碱活性快速检测方法的适应性

为研究集料微观结构对碱活性快速检测方法中对岩石适应性的影响,采用混凝土棱柱体法、快速砂浆棒法、压蒸法、中国快速砂浆棒法研究了波茨坦砂岩的膨胀行为,并研究了膨胀后试件的微观结构.结果表明:快速砂浆棒法、压蒸法、中国快速砂浆棒法均不能正确判定波茨坦砂岩的碱活性,主要是由于这些方法使用的集料中含大量粒径太小、不能反映该砂岩特殊结构特征的颗粒;对该类岩石,除活性组分的类型、数量外,岩石的微观结构特征能够显著影响碱-集料反应发生的位置和膨胀行为.在快速法中采用能够保持岩石原有结构特征的集料粒径是正确鉴定类似波茨坦砂岩微观结构岩石及其它非均质、多矿物岩石碱活性的关键.     

我国首例海工混凝土碱集料反应

对浙江省宁波北仑港海工混凝土构件，用岩相法、扫描电镜／能谱分析、快速压蒸测长法，Ｘ－射线衍射分析等方法进行研究，发现在浪溅区凡表面开裂剥落的混凝土构件中都含有大量的活性集料，并发生了碱集料反应，而表面完整没有裂纹的混凝土构件中活性集料较少；结果表明，海工混凝土如使用碱活性集料，它与来自海水中的碱将会发生反应造成混凝土开裂；碱集料反应和钢筋锈蚀等破坏作用的相互促进，使海工混凝土构件的耐久性大大下降。     

碱矿渣水泥砂浆的碱集料反应膨胀研究

通过测长试验,研究了三类碱矿渣水泥(AASC)砂浆的碱集料反应(AAR)引起的膨胀;分析了碱组分种类、碱质量分数、活性集料质量分数和矿渣种类等因素对AASC砂浆AAR膨胀率的影响.综合宏观和微观测试结果,探讨了碱矿渣混凝土的碱集料反应机理.结果表明,AASC系统出现危险性碱集料反应的可能性远低于普通水泥系统.     

Test methods for evaluating preventive measures for controlling expansion due to alkali-silica reaction in concrete

This paper provides a critical evaluation of the various methods available for testing the efficacy of measures for preventing expansion due to alkali-silica reaction (ASR) in concrete containing deleteriously reactive aggregate. The ideal test method should be rapid, reliable and capable of determining the influence of aggregate reactivity, alkali availability and exposure conditions. None of the currently available or commonly used methods meet all of these criteria. The shortcomings of the different test methods are discussed and suggestions are made for modifying the concrete prism test and accelerated mortar bar test to make these tests more acceptable.     

The effect of supplementary cementing materials on alkali-silica reaction: A review

This paper reviews studies on the effect of supplementary cementing materials (SCM) on alkali-silica reaction (ASR). SCMs control expansion due to ASR by binding alkalis and limiting their availability for reaction with alkali-silica reactive aggregate. The efficacy of the SCM is dependent on the composition of the SCM. Increased amounts of SCM are required to control ASR as its calcium and alkali content increase, as its silica content decreases, as the alkali contributed by the Portland cement increases and as the reactivity of the aggregate increases. There is evidence that the alumina content of the SCM also affects its alkali-binding capacity, however, the precise role and contribution of the alumina is not clear.     

Alkali silica reactivity of agglomerated silica fume

It is commonly accepted that replacement of a portion of cement in mortar or concrete with well-dispersed silica fume reduces expansion caused by alkali silica reaction. Recently there has been much discussion that large, agglomerated particles of silica fume may actually act as alkali silica reactive aggregates, thereby increasing expansion rather than reducing it. The data in the literature, from both field and laboratory studies, are inconsistent. This prompted an extensive laboratory investigation into the alkali silica reactivity of silica fume. Results from accelerated expansion testing and microscopic investigations are presented. It was seen that some agglomerated silica fumes participate in ASR while others do not. Factors determining the reactivity of silica fume agglomerates are suggested.     

Modified model of alkali-silica reaction

Experimental studies have been carried out for understanding why soft and fluid hydrated alkali silicate generated by the alkali-silica reaction (ASR) of aggregate with alkaline pore solution accumulates the expansive pressure for cracking the aggregate and the surrounding concrete. The elemental analysis of aggregate (andesite) embedded in a cement paste has revealed that the alkali silicate has no ability of generating expansive pressure unless the aggregate is tightly packed with a reaction rim. The reaction rim is slowly generated from the alkali silicate that covers the ASR-affected aggregate. Consumption of alkali hydroxide by the ASR induces the dissolution of Ca²⁺ ions into the pore solution. The alkali silicate then reacts with Ca⁺ ions to convert to an insoluble tight and rigid reaction rim. The reaction rim allows the penetration of alkaline solution but prevents the leakage of viscous alkali silicate, so that the alkali silicate generated afterward by the ASR is accumulated in the aggregate to give an expansive pressure enough for cracking the aggregate and the surrounding concrete. The ASR of very tiny aggregate such as fly ash and municipal waste incinerator bottom ash may not cause the deterioration of concrete, since the ASR is completed before the formation of reaction rims.     

Lithological influence of aggregate in the alkali-carbonate reaction

The reactivity of carbonate rock with the alkali content of cement, commonly called alkali-carbonate reaction (ACR), has been investigated. Alkali-silica reaction (ASR) can also contribute in the alkali-aggregate reaction (AAR) in carbonate rock, mainly due to micro- and crypto-crystalline quartz or clay content in carbonate aggregate. Both ACR and ASR can occur in the same system, as has been also evidenced on this paper.Carbonate aggregate samples were selected using lithological reactivity criteria, taking into account the presence of dedolomitization, partial dolomitization, micro- and crypto-crystalline quartz. Selected rocks include calcitic dolostone with chert (CDX), calcitic dolostone with dedolomitization (CDD), limestone with chert (LX), marly calcitic dolostone with partial dolomitization (CD), high-porosity ferric dolostone with clays (FD). To evaluate the reactivity, aggregates were studied using expansion tests following RILEM AAR-2, AAR-5, a modification using LiOH AAR-5Li was also tested. A complementary study was done using petrographic monitoring with polarised light microscopy on aggregates immersed in NaOH and LiOH solutions after different ages. SEM-EDAX has been used to identify the presence of brucite as a product of dedolomitization. An ACR reaction showed shrinkage of the mortar bars in alkaline solutions explained by induced dedolomitization, while an ASR process typically displayed expansion. Neither shrinkage nor expansion was observed when mortar bars were immersed in solutions of lithium hydroxide.Carbonate aggregate classification with AAR pathology risk has been elaborated based on mechanical behaviours by expansion and shrinkage. It is proposed to be used as a petrographic method for AAR diagnosis to complement the RILEM AAR1 specifically for carbonate aggregate. Aggregate materials can be classified as I (non-reactive), II (potentially reactive), and III (probably reactive), considering induced dedolomitization ACR (dedolomitization degree) and ASR.     

Microstructure of selected aggregate quartz by XRD,and a critical review of the crystallinity index

Reliable assessment of the potential of quartz in aggregate to develop deleterious alkali–silica reaction (ASR) is essential for the construction of durable concrete. The crystallinity index for quartz (QCI) introduced by Murata and Norman [15] has been applied to predict the ASR potential of quartz. Despite a number of technical shortcomings and omissions in the original paper, the method has arguably become the most popular alternative for the ‘petrography + expansion testing’ combo.This paper investigates the ASR potential of twelve Italian concrete aggregates, by petrography, mortar bar expansion testing, and test the quartz potential reactivity by calculating the QCI and by the line profile analysis of the XRD pattern. The results confirm that a relationship between QCI values and aggregate expansion behavior is absent. Contrary, the microstructural analysis is a powerful method for predicting the ASR-reactivity of quartz. Finally, the method introduced by Murata and Norman [15] is critically reviewed.     

不同养护条件下含石英玻璃地质聚合物砂浆的变形行为

为阐明典型活性组分（无定型SiO2）在地质聚合物中的作用行为和效应,探索地质聚合物体系中碱-集料反应评价方法,研究常温（23℃）和38℃湿气养护（相对湿度〉95%）、80℃在1 mol/L NaOH溶液浸泡及150℃在10%（质量分数）的KOH溶液压蒸下,含石英玻璃集料地质聚合物砂浆的变形行为,采用扫描电镜、电子散射能谱研究产物的组成和微观结构。结果表明：4种养护条件下,特别是在传统普通硅酸盐水泥（OPC）体系所规定的养护条件和龄期内,含石英玻璃集料地质聚合物砂浆没有发生有害膨胀;但是随养护条件不同,地质聚合物基体和石英玻璃可能经历不同的化学反应过程,进而导致不同的变形行为,特别是在高温且有外碱介入时,地质聚合物基体在后期会产生膨胀效应。不宜采用单一的适于OPC体系的高温、高碱快速检测混凝土碱-集料反应的检测方法来评价地质聚合物体系中的碱-集料反应行为。     

A rapid method for identification of alkali reactivity of aggregate

A rapid method for the identification of alkali reactivity of aggregate within two days has beeb achieved. 1×1×4 cm mortar bars with cement:aggregate = 10:1, w/c = 0.3, size of aggregate = 0.15?0.75mm were demolded after one-day curing and subjected subsequently to 100°C steam curing for 4 hours, after which they were immersed in 10% KOH solution and autoclave-treated at 150°C for 6 hours. After each stage of curing expansion measurements were carried out. From the data of more than thirty species of rocks, the authors arrived at the conclusion that the rapid method could be used to distinguish reactive and non-reactive aggregate. The results of microscopic observation made clear that the expansion of mortar bars was caused by alkali-silica reaction. This method cannot only be used to identify the alkali reactivity of aggregate, but when combined with the use of optic and electron microscope, can be also used to study the mechanism of alkali-aggregate reaction.     

胶砂比和集料级配对ASR膨胀的影响

为建立快速鉴定硅质集料碱活性的方法 ,以沸石化珍珠岩和硅质砾石为集料研究了胶砂比和集料级配对砂浆试体ASR膨胀的影响。结果表明 :对检测集料ASR活性而言 ,快速砂浆棒法 (ASTMC12 6 0和CSAA2 3 2 - 2 5A)所建立的集料级配和胶砂比不是最敏感条件。采用单级配集料和多胶砂比砂浆试体可以更快速、可靠地鉴定集料ASR活性     

Alkali–silica reactions (ASR): Literature review on parameters influencing laboratory performance testing

Utilisation of potentially alkali–silica reactive aggregates requires reliable performance tests to evaluate the alkali–silica reactivity of various aggregate combinations, including their alkali threshold dependence on binder type. Several such performance tests have been used worldwide for more than 15 years, but none of the methods have proven to be reliable for use with all aggregate types and all binders. One of the objectives of RILEM TC 219-ACS (2007–2012) is to develop and validate one or more of such performance tests.Several parameters may influence the results obtained in an accelerated performance test compared to the field behaviour. Based on a state of the art literature review, this paper discusses which parameters must be considered to be able to develop reliable ASR performance testing methods and provides some tentative recommendations. The internal humidity in the test specimens, the extent of alkali leaching and the storage temperature are of particular importance.