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Investigation on Preparation and Application in Concrete of Physically Modified Fly Ash 物理改性粉煤灰的制备及在混凝土中的应用研究
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2024-02-17 DOI: 10.3151/jact.22.77
Sun Zhisheng, Zhu Wenshang, Ma Zhaomo, Wang Xingqin, Yang Zhongmao, Zou Chunye, Huang Qin, Feng Xianxu, Rao Zhengtang

Raw fly ash (RFA) was modified by a self-developed new dry energy-saving vertical grinding mill. This was beneficial to improve the particle morphology and distribution of RFA and enhanced its practical applicability in cement and concrete. The physical modification mechanism of RFA was elucidated by simulating the grinding process, and the physical properties and the application performance of modified fly ash (MFA) were characterized. The results demonstrated that the new grinder can effectively realize the physical modification of RFA and significantly improve its properties because the porous structure and the intactness of glass beads of RFA are preserved without being destroyed. The fineness of MFA was improved to the standard of Class I or II fly ash, the 28 d strength activity index of which was increased by 7% to 17%. The fluidity of mortar was also improved by 15 to 34 mm. In addition, the water requirement ratio can be significantly reduced when MFA is used to prepare C30 and C45 concrete. The 28 d strength of concrete with 50% content of MFA was increased by 23.76% and 15.84%, respectively. These results suggest that the grinding process studied here is a novel method for improving the performance of MFA.

采用自主研发的新型干法节能立磨对生料粉煤灰(RFA)进行改性。这有利于改善 RFA 的颗粒形态和分布,提高其在水泥和混凝土中的实用性。通过模拟粉磨过程,阐明了 RFA 的物理改性机理,并对改性粉煤灰(MFA)的物理性质和应用性能进行了表征。结果表明,新型研磨机能有效实现对 RFA 的物理改性,并显著改善其性能,因为 RFA 的多孔结构和玻璃微珠的完好性没有被破坏。MFA 的细度提高到了 I 级或 II 级粉煤灰的标准,其 28 d 强度活性指数提高了 7% 至 17%。砂浆的流动性也提高了 15 至 34 毫米。此外,用 MFA 配制 C30 和 C45 混凝土时,可显著降低需水量比。含 50% MFA 的混凝土 28 d 强度分别提高了 23.76% 和 15.84%。这些结果表明,本文研究的研磨工艺是提高 MFA 性能的一种新方法。
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引用次数: 0
Development of Post-installed Headed Bars Embedded into Grouted Holes with Enlarged Ends 将后安装封头钢筋嵌入扩大端部的灌浆孔中的发展情况
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2024-01-24 DOI: 10.3151/jact.22.62
Hassane Ousalem, Gin Horiuchi, Akitoshi Hamada, Hiroto Takatsu, Yuki Idosako, Hiroyuki Masuda, Yuki Hiroshima

To secure good quality post-installed anchors with a relatively short anchorage length and sufficient pull-out/shear resistance, an anchoring method with enlarged diameter at the end of drilled holes has been developed. Anchors were provided with head plates and fixed into the enlarged holes using non-shrinkage high-strength cementitious grout. Pull-out and shear preliminary tests were conducted to investigate the behavior and evaluate the strength of such anchors set in concrete. Furthermore, an evaluation method, based on the Japanese recommendations for design of composite constructions, was proposed. The evaluated pullout and shear capacities of all tested anchors designed to fail by steel yielding ensured sufficient safety margin as to test results, whereas those of some anchors designed to fail by concrete cone breakout should be reduced.

为了确保高质量的后安装锚固件具有相对较短的锚固长度和足够的抗拉/抗剪能力,开发了一种在钻孔末端扩大直径的锚固方法。锚杆配有顶板,并使用无收缩高强度水泥基灌浆料固定在扩大的孔中。进行了拉出和剪切初步试验,以研究这种锚固在混凝土中的行为并评估其强度。此外,还提出了一种基于日本复合结构设计建议的评估方法。所有测试锚栓的评估拉拔和剪切能力都被设计为通过钢屈服失效,确保了测试结果有足够的安全系数,而一些锚栓的评估拉拔和剪切能力则被设计为通过混凝土锥体破裂失效,因此应降低其评估拉拔和剪切能力。
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引用次数: 0
Experimental Study of Bonding Performance of Post-installed Rebar Anchors under Unilateral Pressure 后安装钢筋锚固件在单侧压力下的粘结性能实验研究
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2024-01-23 DOI: 10.3151/jact.22.47
Ning-yu Zhao, Ailin Yang, Hao Liu, Yi Song, Haifei Jiang

Post-installed rebar (PIR) is extensively utilized for rehabilitating, strengthening, and retrofitting existing concrete structures, and its anchorage design greatly concerns the failure mode and tensile behavior. PIR anchored in joints or columns generally suffers pressures normal to its anchorage section in one direction, and PIR's failure mode and tensile behavior can be greatly affected. However, limited research on the unilateral pressure effect for PIR has been conducted, with remaining uncertainties on applications and designs for PIR. Thus, this paper carried out the pull-out tests of 38 specimens with various anchorage conditions (20 unilateral pressure specimens, 14 no-lateral pressure specimens, and four bilateral pressure specimens) to investigate the bond behavior for PIR subjected to unilateral pressure. Besides, the effects of concrete strength, rebar diameter, and anchorage length on PIR under unilateral pressure were also considered in the tests. The test results showed that the no-lateral pressure specimens split in the concrete and adhesive layer. In contrast, the unilateral and bilateral pressure specimens occurred two typical failures [adhesive-rebar (A-R) interface failure and adhesive fracture failure]. In addition, the interfacial damage and cracking pattern were discussed in detail. Then, the bond strength and bond slip of specimens were investigated. The result showed that the bond strength under unilateral pressure was greater than that under no-lateral pressure but less than that under bilateral pressure, and there was no obvious change in bond strength while the unilateral pressure increased. Regarding bond slip, it was found that the bond slip increased with the bond strength. This paper performed an experimental investigation on failure modes and cracking patterns for PIR under unilateral pressure. It analyzed the unilateral pressure effect on the bond performance for PIR, raising the safety considerations about PIR applications in load-bearing structures.

后置钢筋(PIR)被广泛用于现有混凝土结构的修复、加固和改造,其锚固设计在很大程度上关系到其破坏模式和拉伸行为。锚固在接缝或柱中的 PIR 通常会承受其锚固截面法向的单向压力,PIR 的破坏模式和拉伸行为会受到很大影响。然而,对 PIR 单侧压力效应的研究还很有限,PIR 的应用和设计仍存在不确定性。因此,本文对 38 个不同锚固条件的试件(20 个单侧压力试件、14 个无侧压试件和 4 个双侧压力试件)进行了拉拔试验,以研究 PIR 在单侧压力作用下的粘结行为。此外,试验还考虑了混凝土强度、钢筋直径和锚固长度对单侧压力下 PIR 的影响。试验结果表明,无侧压试样在混凝土层和粘合剂层出现裂缝。相比之下,单侧和双侧压力试样出现了两种典型的失效(粘合剂-钢筋(A-R)界面失效和粘合剂断裂失效)。此外,还详细讨论了界面破坏和开裂模式。然后,研究了试样的粘接强度和粘接滑移。结果表明,单侧压力下的粘接强度大于无侧压力下的粘接强度,但小于双侧压力下的粘接强度,且单侧压力增加时粘接强度无明显变化。在粘接滑移方面,研究发现粘接滑移随粘接强度的增加而增加。本文对单侧压力下 PIR 的破坏模式和开裂模式进行了实验研究。它分析了单侧压力对 PIR 粘接性能的影响,提出了在承重结构中应用 PIR 的安全考虑。
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引用次数: 0
Multi-exponential Inversion of the Relaxometry Data of Low-field Nuclear Magnetic Resonance for Cement-based Materials 水泥基材料低场核磁共振弛豫测量数据的多指数反演
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2024-01-20 DOI: 10.3151/jact.22.33
Xiaoyu Zhang, Chunsheng Zhou, Jing Qiao, Le Li, Lizhi Xiao

Low-field Nuclear Magnetic Resonance (LF-NMR) technique has been attracting increasing concern in nondestructively characterising cement-based materials (CBMs), whose nanoscale pore structure are sensitive to water removal. In order to achieve the multi-exponential inversion of relaxometry data preferred by the interpretation on local pore structure of CBMs, an algorithm incorporating L1 regularisation with capability of yielding sparse solution is developed with the aids of Interior-Point method and various principles for optimising the regularisation parameter. Numerical analyses on representative cases show that, the proposed algorithm equipped with the Morozov discrepancy principle is capable of resolving all artificially designed exponential components of various intensities with satisfactory accuracy and precision, even at relatively low signal-to-noise ratio. When applying to resolve the relaxometry data obtained on a cement paste, the algorithm is good at characterising its pore structure with clear significance and capturing its detailed evolution during curing under hot water with good precision.

低场核磁共振(LF-NMR)技术在无损表征水泥基材料(CBMs)方面日益受到关注,因为水泥基材料的纳米级孔隙结构对水的去除非常敏感。为了实现弛豫测量数据的多指数反演,以解释 CBMs 的局部孔隙结构,我们开发了一种结合 L1 正则化的算法,该算法具有生成稀疏解的能力,并借助了内部点法和各种优化正则化参数的原理。对代表性案例的数值分析表明,所提出的算法配备了莫罗佐夫差异原理,即使在信噪比相对较低的情况下,也能以令人满意的精度和准确度解析所有人工设计的各种强度的指数成分。当应用该算法解析水泥浆弛豫测定数据时,该算法能很好地描述水泥浆的孔隙结构,并能准确捕捉其在热水固化过程中的详细演变。
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引用次数: 0
Effect of Temperature on the Early-age Hydration and Setting Behaviour of Mixes Containing GGBS 温度对含 GGBS 混合料早期水化和凝结行为的影响
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2024-01-12 DOI: 10.3151/jact.22.14
Fragkoulis Kanavaris, Marios Soutsos, Jian-Fei Chen

Over the past years there has been an increasing trend to use supplementary cementitious materials in concrete to improve its sustainability credentials and durability properties. Perhaps amongst the most popular supplementary cementitious materials is ground granulated blast-furnace slag (GGBS). While the hydration and setting characteristics of mixes with GGBS cured under standard conditions (20°C) has been adequately investigated, the effect of temperature on heat of hydration and setting and the interrelation of these properties has not been evaluated for GGBS containing mixes. In this study, the heat of hydration and setting behaviour of mixes with various levels of GGBS (0, 20, 35, 50 and 70%) cured under elevated temperatures (20, 30, 40, 50 and 60°C) is determined. Elevated curing temperature accelerates the hydration reactions and can significantly reduce the setting time of GGBS-containing mixes. The investigation of heat of hydration at very early ages, can provide an indication of the initial and final setting times of cementitious mixes. The “apparent” activation energy used to characterise temperature sensitivity of cementitious systems, is calculated based on heat of hydration and setting time measurements. It was found that the “apparent” activation energy increases with GGBS content for both heat of hydration and setting behaviour. The value of “apparent” activation energy differs significantly depending on the material property that is considered, such as compressive strength, heat of hydration or setting time.

过去几年来,在混凝土中使用辅助胶凝材料以提高其可持续性和耐久性的趋势越来越明显。其中最受欢迎的辅助胶凝材料可能就是磨细高炉矿渣(GGBS)。虽然对在标准条件(20°C)下养护的含 GGBS 混合料的水化和凝结特性进行了充分研究,但对含 GGBS 混合料而言,温度对水化热和凝结的影响以及这些特性之间的相互关系尚未进行评估。本研究确定了在高温(20、30、40、50 和 60°C)条件下固化的含有不同含量 GGBS(0、20、35、50 和 70%)的混合料的水化热和凝结性能。固化温度升高会加速水化反应,并能显著缩短含 GGBS 混合料的固化时间。对早期龄期的水化热进行研究,可为水泥基混合料的初凝和终凝时间提供指示。用于描述水泥基系统温度敏感性的 "表观 "活化能是根据水化热和凝结时间测量值计算得出的。研究发现,在水化热和凝结行为方面,"表观 "活化能随 GGBS 含量的增加而增加。表观 "活化能的数值因所考虑的材料特性(如抗压强度、水化热或凝结时间)而有很大不同。
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引用次数: 0
Shear Behaviour of RC Beams Strengthened using CFRP Grid-ECC/PMM Matrix Composites: An Experimental and Numerical Investigation 使用 CFRP 网格-ECC/PMM 矩阵复合材料加固的 RC 梁的剪切行为:实验与数值研究
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2024-01-07 DOI: 10.3151/jact.22.1
Xu Yang, Jun-Qi Huang

In recent advancements, a novel strengthening approach employing engineered cementitious composites (ECC) and fibre-reinforced polymer (FRP) materials has emerged. This method integrates ECC as the matrix, carbon fibre-reinforced polymer (CFRP) grid as the internal strengthening component, and epoxy resin for bonding the overlay to the concrete substrate. This study conducted tests on four reinforced concrete (RC) beams under a four-point load configuration. One beam served as an un-strengthened control specimen, while three were subjected to different shear strengthening methods: polymer-modified mortar (PMM), ECC, and CFRP grid-reinforced ECC matrix composites layer (FGREM). The investigation covered failure modes, load-deformation relationships, and load-strain relationships. Finite element (FE) analysis was employed to reproduce the test results. Key findings include the ability of ECC as a matrix to substantially reduce concentrated interfacial bond stresses, preventing debonding failure. The FGREM-strengthened specimen exhibited a failure mode characterized by side concrete cover separation, resulting in a notable 124% enhancement in shear resistance. The proposed FE model, incorporating interfacial behaviour, accurately simulated the performance of all specimens.

最近,出现了一种采用工程水泥基复合材料(ECC)和纤维增强聚合物(FRP)材料的新型加固方法。这种方法将工程水泥基复合材料(ECC)作为基体,碳纤维增强聚合物(CFRP)网格作为内部增强部件,环氧树脂用于将覆盖层粘合到混凝土基体上。本研究在四点荷载配置下对四根钢筋混凝土(RC)梁进行了测试。其中一根梁作为未加固的对照试样,另外三根梁则采用了不同的剪切加固方法:聚合物改性砂浆(PMM)、ECC 和 CFRP 网格加固 ECC 矩阵复合材料层(FGREM)。调查内容包括失效模式、荷载-变形关系和荷载-应变关系。采用有限元(FE)分析来再现测试结果。主要发现包括 ECC 作为基体能够大幅降低集中的界面粘接应力,防止脱粘失效。经 FGREM 加固的试样表现出一种以侧混凝土覆盖层分离为特征的破坏模式,从而显著提高了 124% 的抗剪能力。所提出的包含界面行为的有限元模型准确地模拟了所有试样的性能。
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引用次数: 0
Probabilistic Service Life Prediction of Alkali Activated Concretes Exposed to Chloride Induced Corrosion 暴露于氯化物诱导腐蚀的碱活性混凝土使用寿命概率预测
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2023-12-26 DOI: 10.3151/jact.21.1020
Tamara Janey Chidiac, Neven Ukrainczyk, Dale P. Prentice, John L. Provis

In this study, the well-established service life design code defined in fib Bulletin 34 is adapted to predict the time to initiation of reinforcement corrosion in alkali-activated concretes submerged in marine conditions. The model approach is based on the probabilistic calculation of the time needed for a critical concentration of chloride ions, migrating from the external environment towards the rebar, to accumulate at the surface of the steel reinforcement and initiate the corrosion reaction. The information required to define the parameters of the model is derived from literature data, relating the concrete mix designs with accelerated laboratory test results. The findings indicate that alkali-activated concretes with high calcium content can exhibit promising characteristics as a construction material applied for structural application in chloride-rich corrosive environments. The probabilistic approach adopted in this model provides the opportunity to assess the influence of variability in mineralogical composition and reactivity of the precursors with the alkaline activating solution, that influence the chemical evolution and microstructure of the binder matrix. The predicted service life is quite sensitive to these factors, with very high service lives predicted for some alkali-activated concretes but rather short service lives predicted for others, and this must be incorporated into any engineering assessment of future material performance.

在本研究中,对 fib Bulletin 34 中定义的行之有效的使用寿命设计规范进行了调整,以预测浸没在海洋条件下的碱活性混凝土中钢筋开始锈蚀的时间。该模型方法基于对从外部环境向钢筋迁移的氯离子临界浓度在钢筋表面积累并引发腐蚀反应所需时间的概率计算。定义模型参数所需的信息来自文献数据,这些数据与混凝土混合设计和实验室加速测试结果相关。研究结果表明,钙含量高的碱活性混凝土作为一种建筑材料,在富含氯化物的腐蚀环境中的结构应用中表现出良好的特性。该模型采用的概率方法提供了一个机会,可以评估矿物成分的变化和前体与碱性活化溶液的反应性的影响,这些都会影响粘结剂基体的化学演变和微观结构。预测的使用寿命对这些因素相当敏感,一些碱活化混凝土的预测使用寿命非常高,而其他混凝土的预测使用寿命则相当短,这一点必须纳入对未来材料性能的任何工程评估中。
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引用次数: 0
Effects of Lime-Based Expansion Material and Freeze-Thaw Cycles on Air-Void Blockage in Concrete 石灰基膨胀材料和冻融循环对混凝土气泡堵塞的影响
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2023-12-19 DOI: 10.3151/jact.21.1008
Hidehiko Ogata, Momona Otsuka, Masahiro Hyodo, Haruka Ikadatsu

Air voids in concrete are sometimes observed to be blocked by white precipitates. In this study, the authors conducted freeze-thaw tests on concrete mixed with lime-based expansion material and then performed microscopic observations using scanning electron microscopy, elemental analysis using energy-dispersive X-ray spectroscopy. The size distributions of air voids in the concrete during the curing period (28 days after placement) and before, during, and after the tests were also measured in order to investigate the effects of the expansion material on air-void blockage as well as the underlying processes. During the curing period, no air-void blockage was observed. However, as the concrete aged, precipitates formed on the inner surfaces of the air voids. During the freeze-thaw tests, the number of air voids with diameters of ≤0.15 mm decreased, and the air-void spacing factor increased as the relative dynamic modulus of elasticity decreased. It was found that freeze-thaw cycles caused calcium-based precipitates to form inside the air voids of concrete mixed-with lime-based expansion material, and that the air voids became blocked.

混凝土中的空气空隙有时会被白色沉淀物堵塞。在这项研究中,作者对掺有石灰膨胀材料的混凝土进行了冻融试验,然后使用扫描电子显微镜进行了微观观察,并使用能量色散 X 射线光谱进行了元素分析。此外,还测量了混凝土在养护期(浇筑后 28 天)以及试验前、试验中和试验后的气孔大小分布,以研究膨胀材料对气孔堵塞的影响以及其基本过程。在养护期间,没有观察到气泡堵塞现象。然而,随着混凝土的老化,气隙内表面形成了沉淀物。在冻融试验中,直径≤0.15 毫米的气孔数量减少,气孔间距系数随着相对动态弹性模量的降低而增大。研究发现,冻融循环导致掺有石灰膨胀材料的混凝土空隙内形成钙基沉淀物,空隙被堵塞。
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引用次数: 0
The Influences and Effect Mechanism of Low Temperature Curing on the Performances of Basic Magnesium Sulfate Cement 低温固化对碱式硫酸镁水泥性能的影响及作用机制
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2023-12-13 DOI: 10.3151/jact.21.995
Keyue Fang, Chengyou Wu, Hongdu Chen

Due to lightweight, high-strength, and high toughness properties, Basic magnesium sulfate cement (BMSC) can be widely used in producing various structural and decorative products. Most current research only focuses on the performance of BMSC under room temperature. However, low temperature environments may have a serious impact on the performance of BMSC, such as during cold seasons or in salt lake cold regions with abundant magnesium resources, so the performance of BMSC in low temperature environment needs to be explored to expand its application. This study investigated the influence of different low temperatures (−5 to 20°C) on the compressive strength and water resistance of BMSC cement. The phase composition, microstructure and pore structure of BMSC has been analyzed using XRD, QXRD, TG/DTA, SEM, BSEM/EDS Mapping and MIP. The Results indicate that the low hydration rate, precipitation of magnesium sulfate, increase in porosity and decrease in 517 phase content are the main reasons for the low strength of BMSC under low temperature curing. Although hardened BMSCs cured at low temperatures can continue to hydrate in water to form strength phases, corrosion and cracking may occur. Replacing light burned magnesite with high active magnesium oxide can significantly improve the mechanical properties of low temperature cured BMSC. However, low temperatures reduced the crystallinity of the 517 phase, thereby increasing its water solubility and lead to poor water resistance of BMSC.

碱式硫酸镁水泥(BMSC)具有轻质、高强度和高韧性等特性,可广泛用于生产各种结构和装饰产品。目前大多数研究只关注 BMSC 在室温下的性能。然而,低温环境可能会对硫酸镁水泥的性能产生严重影响,例如在寒冷季节或镁资源丰富的盐湖寒冷地区,因此需要探索硫酸镁水泥在低温环境下的性能,以扩大其应用范围。本研究探讨了不同低温(-5 至 20°C)对 BMSC 水泥抗压强度和耐水性的影响。使用 XRD、QXRD、TG/DTA、SEM、BSEM/EDS 制图和 MIP 分析了 BMSC 的相组成、微观结构和孔隙结构。结果表明,水化率低、硫酸镁析出、孔隙率增加和 517 相含量减少是低温固化下 BMSC 强度低的主要原因。虽然低温固化的硬化 BMSC 可继续在水中水化形成强度相,但可能会发生腐蚀和开裂。用高活性氧化镁替代轻烧菱镁矿可显著改善低温固化 BMSC 的机械性能。然而,低温会降低 517 相的结晶度,从而增加其水溶性,导致 BMSC 的耐水性变差。
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引用次数: 0
Hydration Mechanism of Portland and Calcium Sulphoaluminate Cementitious Material 硅酸盐和硫铝酸钙水泥基材料的水化机理
IF 2 4区 工程技术 Q2 Engineering Pub Date : 2023-12-13 DOI: 10.3151/jact.21.983
Jiahe Wang, Yanbin Tan, Huajian Li, Yongjiang Xie, Zhongwei Feng

This paper discusses the hydration process of Portland cement (PC) and Calcium Sulphoaluminate cement (CSA) composite material at the early age. The setting time and mortar strength were tested, the hydration process was analyzed by isothermal calorimetry tests, and the hydration products were characterized by XRD, SEM analysis. The results show that: CSA can significantly improve the hydration rate of ultra-early age (2 h and 6 h) and improve the mechanical properties. But there are still interactions between the hydration of PC and CSA, including that the gypsum in CSA will inhibit the hydration of C3A in PC and the CH generated by PC will promote the rehydration of AH3. The inhibiting or promoting effect of CSA on hydration process changes with its content. The design method of PC-CSA composite material was proposed, and the reasonable mixing amount of PC or CSA was also suggested.

本文讨论了硅酸盐水泥(PC)和硫铝酸钙水泥(CSA)复合材料在龄期的水化过程。测试了凝结时间和砂浆强度,通过等温量热试验分析了水化过程,并通过 XRD 和 SEM 分析对水化产物进行了表征。结果表明CSA 能明显提高超早期龄期(2 h 和 6 h)的水化速率,改善力学性能。但 PC 与 CSA 的水化仍存在相互作用,包括 CSA 中的石膏会抑制 PC 中 C3A 的水化,而 PC 产生的 CH 会促进 AH3 的再水化。CSA 对水化过程的抑制或促进作用随其含量的变化而变化。提出了 PC-CSA 复合材料的设计方法,以及 PC 或 CSA 的合理混合量。
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引用次数: 0
期刊
Journal of Advanced Concrete Technology
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