粉煤灰混凝土早期碳化规律研究

选取粉煤灰掺量为0、10%、20%和30%,混凝土强度为C30、C40和C50的粉煤灰混凝土为研究对象,通过试验得到了粉煤灰混凝土浇筑后300天内自然条件下的碳化发展规律,分析研究了养护时间及不同浇筑面早期碳化发展的差异,建立了粉煤灰混凝土早期碳化深度的计算模型.结果表明:粉煤灰混凝土的早期碳化深度增长随养护时间的延长而减慢,碳化深度随粉煤灰掺量的增加而增大;浇筑顶面的碳化深度最大而底面的碳化深度最小.     

掺粉煤灰水泥混凝土的自然碳化

在实验室测定了掺粉煤灰水泥混凝土在自然条件下的碳化规律,历时5年。通过试验,发现,混凝土的碳化过程是很复杂的,特别是掺粉煤灰水泥混凝土。本文揭示了影响掺粉煤灰水泥混凝土碳化的主要因素,提出了碳化方程及参数。作者还陈述了对混凝土碳化问题的看法。     

大掺量粉煤灰混凝土抵抗碳化和钢筋锈蚀研究

通过在不同胶凝材料用量、不同粉煤灰掺量和不同水胶比下大掺量粉煤灰混凝土碳化和钢筋锈蚀试验,明确了其抵抗碳化和钢筋锈蚀的基本条件.结果显示水胶比是关键条件,只要保证足够低的水胶比,大掺量粉煤灰混凝土具有优异的耐久性.     

混凝土自然碳化及其与人工加速碳化的相关性研究

在实验室研究了普通水泥混凝土和掺粉煤灰水泥混凝土在自然条件下的碳化规律,历时10年。提出了混凝土的碳化方程及其参数。通过自然碳化及相应的人工加速碳化试验和微观测试方法,对混凝土的碳化进程、孔结构和物相变化规律进行了分析。发现了自然碳化与人工加速碳化之间存在的相关性。得出的相关公式可用于碳化速率系数的计算和碳化进程的预测。     

矿物掺和料对混凝土抗渗和抗碳化性能影响的研究

通过试验,研究了不同标准养护时间和湿度下,矿渣粉替代粉煤灰比例对混凝土吸水率、氯离子渗透系数和不同碳化龄期碳化深度的影响.试验结果表明,养护时间越长,养护湿度越大,混凝土的抗渗性能和抗碳化性能越好;随着矿渣粉替代比例的增多,混凝土抗渗性能和抗碳化性能逐渐增强,当替代比例超过60%时,混凝土的抗渗性能和抗碳化性能会得到明显改善;碳化深度和吸水率之间有较好的线性相关性,当矿渣粉替代比例超过40%时,回归系数k值会明显减小.所以,矿渣粉替代粉煤灰比例不宜小于60%.     

碱激发复合渣体混凝土的试验研究

为利用碱(水玻璃、氢氧化钠、碳酸钠)激发粉煤灰和其他工业废渣(矿渣、锂渣及硅灰),改变这些渣体在混凝土中传统利用方式,以便更充分发挥这些工业渣体的活性,研究激发剂的种类、矿渣和粉煤灰的比例及粉煤灰和其他工业废渣复合时对混凝土强度的影响.结果表明,利用水玻璃和氢氧化钠复合激发可配制出强度更高的混凝土,当粉煤灰和矿渣的比例为80∶20时,混凝土28 d抗压强度仍可达66 MPa,粉煤灰∶矿渣∶锂渣∶硅灰=50∶30∶15∶5时,在不采用任何特殊措施的条件下,可配制出28 d抗压强度达85 MPa的环境降负性高强混凝土.同时,对这种混凝土的抗碳化性能进行研究,碳化试验表明,强度等级在C60~C80之间的混凝土,无论从保护钢筋的角度还是碳化后强度的变化情况考虑,其抗碳化性完全可以满足一般建筑的要求.     

粉煤灰高性能混凝土的护筋性

粉煤灰高性能混凝土具有一系列优点,如高密实度、低渗透性、低干缩、较好的抗碳化性能以及粉煤灰的稳定行为等。这些优点赋予粉煤灰高性能混凝土良好的护筋性。     

粉煤灰对混凝土耐久性的影响

分析粉煤灰对混凝土的抗渗，抗冻性，抗碳化性，抗侵蚀性和对碱－集料反应的影响，说明了在混凝土中掺加适量的粉煤灰是提高混凝土耐久性的重要措施。     

粉煤灰高性能混凝土的护筋性

粉煤灰高性能混凝土具有一系列优点,如高密实度、低渗透性、低干缩、较好的抗碳化性能以及粉煤灰的稳定行为等。这些优点赋予粉煤灰高性能混凝土良好的护筋性。     

粉煤灰混凝土耐久性探讨

比较分析各国对粉煤灰混凝土的渗透性、氯离子扩散系数及抗硫酸盐腐蚀的性能、碳化与抗冻性研究,指出粉煤灰混凝土的渗透性比普通混凝土大,但其在水中养护时间较长时,渗透性会降低,但粉煤灰混凝土的氯离子扩散系数比普通混凝土低,因此,用于海洋工程是大有希望的．利用深圳和东莞地区的粉煤灰作为掺合料制备混凝土以达到抗海水侵蚀的效果急待深入研究．     

Durability of lining concrete of subsea tunnel under combined action of freeze-thaw cycle and carbonation

Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete.Under the combined action of freeze-thaw cycle and carbonation,the durability of lining concrete decreases.The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted.For the high performance concrete with proposed mix ratio,the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating.Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.     

Carbonation of sulphoaluminate cement with layered double hydroxides

The increasing importance of the ecologically minded production of building materials makes it necessary to develop reasonable alternatives to the CO2-intense production of ordinary Portland cement （OPC）. The development of new or modified concrete is an important part of existing strategies to improve performance and minimize life-cycle costs. Therefore, we investigated carbonation resistance properties of sulphoaluminate cement （SAC） concrete incorporating layered double hydroxides （LDHs）. X-ray diffraction （XRD） and IR-spectroscopy were employed to characterize the component and structural changes of LDHs and cement paste before and after carbonation test. Carbonation resistance of concrete was experimentally evaluated. Finally, carbonation of Portland cement and SAC concrete was compared. The experimental results show that carbonation depth decreases remarkably with the addition of LDHs, especially the calcinated LDHs. Carbonation depth of SAC concrete is smaller than that of PC concrete regardless of curing time.     

不同材料对碱激发混凝土抗碳化性能影响研究

针对碱激发材料存在抗碳化性能差等缺点,以及对碱激发材料的碳化研究手段还缺乏统一标准。提出了一种硬化混凝土粉末碳化测试方法,结合不同掺量的草木灰、氧化镁、乳酸钠、煅烧水滑石(C-HT)的碱激发矿渣-粉煤灰砂浆(AAM)的抗碳化性能进行研究。试验结果表明:添加草木灰时,AAM抗碳化性能下降,但随着其掺量增加,AAM抗碳化性能逐渐提高,掺量为6%时,AAM抗碳化性能与对照组相差较小;氧化镁、乳酸钠、C-HT均可提高AAM的抗碳化性能,添加6%氧化镁或6%C-HT的效果最明显;乳酸钠对于AAM抗碳化性能提高并不显著。硬化粉末碳化测试方法不仅用于测试AAM的抗碳化性能,而且可以利用碳化程度和速率对不同添加剂进行抗碳化性能的精确对比。     

Research on the Influence of Steam Curing on Properties of C50 Shield Segment Concrete

The effects of steam curing on mechanical properties,drying shrinkage,cracking sensitivity,anti-permeability,and carbonation resistance of C50 shield segment concrete were investigated,which were compared with the standard curing conditions. The results indicated that steam curing could increase early strength of concrete and reduce its drying shrinkage. However,steam curing reduced later strength of concrete,increased its crack sensitivity and deteriorated its anti-permeability and carbonation resistance. Moreover,the incorporation of fly ash could improve the durability of steam-cured concrete.     

Effects of Curing Condition on the Carbonation of Shrinkage-compensated Concrete

Shrinkage-compensating concrete can enhance the permeability and strength. In addition,expansive admixture can densify concrete to advance the carbonation resistance ability. Due to special quality of ettringite,the relative humidity of curing environment has significant effect on the carbonation rate of concrete. This paper discusses the influence of environmental humidity on carbonation rate of shrinkage-compensating concrete. Four different curing conditions were set up,namely the natural environment (RH 60%),standard environment (RH 90%),early age water curing environment for 3 d and 7 d. After curing in these four environments for 28 d,an accelerated carbonation test was performed. Micro-hardness analysis was used to evaluate surface hardness,which depends on,to a great degree,the carbonation depth. TG-DSC analysis was used to study Ca(OH)2 content gradient in the surface layer of concrete in different environment. The results show that natural condition lead to a relatively worse carbonation degree,curing in water for 3 d is harmful to the carbonation resistance,while curing in water for 7 d lead to an equivalent carbonation degree with standard condition,which show the most improvement to carbonation resistance ability.     

Effect of Isobutyl-triethoxy-silane Penetrative Protective Agent on the Carbonation Resistance of Concrete

Effect of isobutyl-triethoxy-silane penetrative protective agent on the carbonation resistance of the concrete was studied.The concrete specimens for the 28 d accelerated carbonation process were manufactured with w/c of 0.49 and 0.64,both in the presence and absence of silane and mineral admixture.The penetration of isobutyl-triethoxy-silane and the carbonation of concrete were investigated by penetration depth,carbonation depth,XRD,SEM,and pore size distribution.The results showed that concrete compactness played an important role in the silane penetration and carbonation resistance.Penetration depth of silane-treated concrete mainly depended on the compactness of the concrete,and could not remarkably change through the accelerated carbonation process.In the accelerated carbonation process,penetrative protective agent improved the carbonation resistance of the higher compactness concretes but accelerated the carbonization process of the lower compactness concretes.As penetrative protective agent penetrated along the external connectivity pores into concrete not filling the entire surface area,the inorganic film could not fully protect the Ca(OH)_2 phase from carbonation.After 28 d accelerated carbonation,fibrous hydration products disappeared and the surface holes decreased.Due to the formation of carbonized products,the porosity of the concrete surface decreased,especially in high-strength concrete.     

蒸压硅酸盐混凝土的碳化

混凝土在空气中被碳化，是一种难以避免的自然现象，碳化使体积和强度发生变化，碱度下降，从而可能导致混凝土内部结构缺陷的增加和耐久性的严重下降。     

再生混凝土抗碳化性能试验研究及理论分析

通过快速碳化试验,以再生骨料掺量、水灰比、水泥用量、原始混凝土强度和矿物掺合料为影响因素,对再生混凝土的碳化性能进行研究。试验结果表明：再生混凝土的碳化深度随水灰比、再生骨料掺量的增加而减小,随原始混凝土强度的增大和水泥用量的增加而增大,适量添加矿物掺和料能降低再生混凝土的碳化深度,提升其抗碳化性能。在已有的普通混凝土碳化模型研究基础上,结合本试验和中国其他学者的试验数据,建立了再生混凝土碳化深度预测模型,模型预测结果与试验值吻合较好。     

外加剂提高粉煤灰混凝土强度的试验研究

通过对加入外加剂的粉煤灰混凝土强度的试验研究，证明外加剂能够提高粉煤灰混凝土的早期强度和后期强度。     

超临界碳化对水泥基材料性能和孔径结构的影响

为了考察超临界碳化技术在水泥基材料改性方面的应用,研究超临界碳化对水泥基材料微观和宏观性能的影响,基于此设计了超临界二氧化碳碳化试验研究水泥砂浆、水泥净浆和混凝土试件的碳化深度、强度、孔径分布以及二氧化碳吸收量的变化。试验分析表明,超临界碳化可以快速实现水泥基材料的碳化,大幅提高试件强度,改善材料的孔径分布,使材料的中细径孔大幅降低,提高材料的抗渗透能力,为改善重金属等危害废物的水泥基固化效果提供了依据。同时超临界碳化可以将大量二氧化碳转化在碳酸钙中沉淀吸收,具有重要的环境保护意义。