高温低湿的自然养护对混凝土性能的影响

研究了不同养护条件下混凝土的强度及耐久性.结果发现,经自然条件下的高温低湿养护后,混凝土的强度早期增长较快,但后期的抗压强度与轴拉强度均低于标准养护下混凝土的试验值;在自然环境中养护时,混凝土各龄期的极限拉伸值均小于标准养护测定值,且混凝土的抗渗等级与抗冻等级均低于标准养护时混凝土的测试结果.混凝土抗渗性试验结果表明,混凝土的强度等级越低,自然养护对混凝土抗渗性带来的影响越大.     

盐渍土地区输电线路基础混凝土抗硫酸盐腐蚀试验研究

为研究输电线路基础混凝土在硫酸盐腐蚀作用下的劣化规律,以盐渍土地区输电线路不同强度等级混凝土为研究对象,采用硫酸盐干湿循环的试验方法,测试了不同混凝土在标准养护条件和硫酸盐腐蚀条件下混凝土强度变化规律。研究结果表明:标准养护条件下,混凝土强度随龄期增长而提高;硫酸盐腐蚀条件下,混凝土强度随着干湿循环次数增加,表现为先提高后降低的规律,且混凝土强度等级越低,强度出现降低的转折点越早。     

后装拔出法检测混凝土强度测强曲线的试验与研究

通过对不同强度等级和不同龄期的混凝土进行后装拔出力与抗压强度对比试验,建立了后装拔出法检测混凝土强度测强曲线的主要试验研究成果,该测强曲线可在符合一定条件的混凝土强度推定时使用。     

新型混凝土内养护剂的应用研究

试验研究了新型混凝土内养护剂SZ在不同强度等级混凝土中对新拌混凝土工作性能的影响,及不同养护条件下对硬化混凝土力学性能的影响。结果表明,新型混凝土内养护剂SZ在水胶比为0.34、0.39的混凝土中,掺量为胶凝材料质量的0.05%时,通过适当提高减水剂掺量,对新拌混凝土工作性能无影响,并且在3种不同养护条件下均能显著提高混凝土强度。     

基于人工神经网络的同条件混凝土强度预测

同条件养护混凝土试件强度与混凝土的配合比、环境温度、养护时间有密切的关系,它们之间是复杂的非线性关系,采用神经网络模型方法,界定两者之间的关系,可用于实际工程的强度预测。     

高强钢管混凝土强度发展规律试验研究

针对C70,C80,C90高强钢管混凝土,通过抽芯取样、预埋试块及间接养护对比试验,探讨不同龄期外界物理行为对高强混凝土强度的影响;并探讨了不同养护条件下高强钢管混凝土随龄期强度发展规律。结果表明,高强钢管混凝土强度对抽芯取样等外界扰动较为敏感,间接养护可模拟钢管内部混凝土的养护环境,其标准立方体试块抗压强度可作为判定钢管混凝土强度的依据之一;随着龄期的增长,钢管的特定养护环境会使得混凝土强度后期增长较多,达到甚至超过标准养护和"同条件"养护的试块强度。将试验研究成果应用于实际工程,取得了满意的效果。     

养护条件对混凝土成熟度的影响

以混凝土早期性能为研究对象,对不同水灰比、不同养护条件下混凝土的成熟度及成熟度与抗压强度的关系进行了实验考察和分析,结果表明：在不同养护条件下计算出的成熟度与其他方法计算出的成熟度存在一定差别;利用推导出的冬季养护条件下混凝土抗压强度与成熟度的关系式可计算冬季养护条件下混凝土的早期强度。     

混凝土工程的监理验收

针对监理组织混凝土分项工程验收时常遇到的一些问题,如混凝土检验批和混凝土强度验收批的划分、标准养护试件和同条件养护试件、混凝土强度检验的合格评定、混凝土结构实体检验等,根据相关规范进行探讨,并提出了意见和建议。     

Effects of steam curing on strength and porous structure of concrete with low water/binder ratio

A research program was carried out to investigate the effects of duration of initial steam curing at atmosphere pressure on compressive strength of concrete with low water/binder ratio. The results showed that the compressive strength of samples steam cured for 5, 10, 14 h increased, while it decreased distinctively for sample steam cured for 24 h. Mercury intrusion porosimetry (MIP) method and scanning electron microscope-backscattered electron (SEM-BSE) image analysis technique were adopted to measure the corresponding variation of porous characteristics caused by the increasing duration of steam curing. The changes in coarse porosity and total porosity calculated by SEM-BSE image analysis and MIP method respectively could indicate the relationship between porosity and mechanical properties of the concrete subjected to different duration of steam curing. Compared with total porosity obtained by MIP method, the coarse porosity by SEM-BSE image analysis was in better accord with the compressive strength because the coarse pores measured by SEM-BSE image analysis were larger than 0.5 μm and included not only the interconnected pores but also the closed ones. An empirical model was developed to evaluate the influence of duration of initial steam curing on the compressive strength of concrete. By comparison, the measured compressive strength was in great accordance with the compressive strength calculated by the proposed model.     

养护条件对不同陶粒掺量混凝土强度影响的研究

研究了不同水灰比的普通混凝土、混合骨料混凝土和轻骨料混凝土在不同养护条件下的强度发展规律,同时还对混凝土内部相对湿度进行了测定。结果表明,室外自然养护条件下,普通混凝土28 d后强度几乎不再增长;标准养护条件下,掺加陶粒的低水灰比混凝土后期强度增长率较高;水中养护条件下,陶粒自养护作用对混凝土强度增长的贡献较低。     

Long term study on compressive and bond strength of coconut shell aggregate concrete

Effects of three types of curing on coconut shell aggregate concrete have been studied for long term performance. The pore structure of coconut shell has been studied through scanning electron microscope (SEM). The pore structures in coconut shell behave like a reservoir. Intermittent curing produced the highest coconut shell aggregate concrete strength, followed by full water, and then by air-dry curing. Biological decay was not evident as the concrete cubes gained strength even after 365 days. Up to an age of 90 days, the samples under all types of curing conditions showed improved response on the pulse velocity and subsequently an insignificant drop. The ultimate bond strength of coconut shell aggregate concrete under all types of curing conditions was much higher compared to the theoretical bond strength as per BS 8110 and IS 456. Bonding between the cement paste and the coconut shell aggregate has been studied by measuring fissure between the coconut shell and the cement paste through SEM analysis. It shows a tendency of narrowing the fissure due to its age, which shows that the bond appears to be better between the coconut shell and the cement paste.     

装配式构件高强混凝土制备技术研究

该文以碱矿渣胶凝材料作为胶结材,使用级配合理的普通砂、石集料来制备装配式构件高强混凝土,并采用蒸汽养护制度以加速混凝土的强度发展。文章较全面的研究了裹浆工艺、养护方式、配制参数及碱组分等因素对装配式构件高强混凝土强度的影响,确定了装配式构件高强混凝土的制备技术条件及参数。     

-3℃养护条件下矿物掺合料对混凝土强度和孔隙结构的影响研究

为了研究不同养护条件下矿物掺合料对混凝土强度和孔隙结构的影响,进行-3℃和标准养护条件下,复掺粉煤灰、矿粉和硅灰对混凝土抗压强度、孔隙结构的试验。结果表明:与标准养护相比,在-3℃养护条件下,矿物掺合料的掺入对混凝土抗压强度有下降趋势,但对其孔径均有优化作用。基准组、复掺10%粉煤灰+10%矿粉+1%硅灰组、复掺10%粉煤灰+10%矿粉+3%硅灰组,28 d龄期标准养护下出现细小孔的频率是负温养护1.122~1.259倍,56 d龄期标准养护下出现细小孔的频率是负温养护1.108~1.180倍,矿物掺合料对混凝土硬化含气量和平均气泡间距均有改善作用,在标准养护条件下的优化作用明显优于负温养护条件。     

养护对抗渗混凝土影响的研究

养护不仅影响混凝土的强度,也影响混凝土的渗透性能。氯离子渗透深度是反映混凝土渗透性能高低的一种重要参数。首先设计出四种有代表性的养护条件,研究养护条件对混凝土的抗渗性能的影响。研究结果表明,常温潮湿养护将有利于降低混凝土的氯离子渗透深度,对提高混凝土的抗渗性能有明显效果。然后在给定养护条件下,在混凝土拌合物中掺入硅灰、粉煤灰和养护剂的情况下做出了对比试验,在混凝土板试验的基础上取样并测出氯离子的渗透深度。普通混凝土中掺入硅灰和粉煤灰等矿物掺合料能减少氯离子的渗透深度,表明了混凝土中掺入掺合料来提高抗渗性能是一种可行的途径。最后试验测出的自养护混凝土的氯离子渗透深度相对比较低,它具有优良的抗渗性能,表明了自养护混凝土对提高混凝土抗渗性能有着良好的发展前景。     

多年冻土环境下混凝土灌注桩强度发展规律的研究

本文采用跟踪养护的方法对多年冻土环境下的混凝土强度发展进行了试验模拟．并与标准养护及恒负温养护混凝土强厦发展进行了对比。结果表明：粉煤灰掺量在较低温度范围(0℃～10℃)内等量取代水泥时对混凝土的强度降低很敏感。确定了多年冻土环境下混凝土强厦发展规律的试验方法。     

Integrating embedded piezoelectric sensors with continuous wavelet transforms for real-time concrete curing strength monitoring

It is highly necessary to evaluate strength development during the curing process to ensure the quality of concrete in construction using concrete. In particular, curing strength monitoring at early age is very important to reduce the construction cost and time, because it can provide the information required for the decision-making to safely progress to the next process. In this study, a guided wave-based non-destructive curing strength gain monitoring method that can be used even for early-age concrete is proposed. A steel plate-type piezoelectric sensor module was embedded in the concrete media at the same time as concrete placement to measure the signal from early-age concrete. The guided wave signals were measured continuously using the pitch-catch method at regular intervals. The wavelet transform process was performed to improve the quality of the signal. The guided wave's velocity of each measurement time was varied by extracting the time of flight. The wave velocity hysteresis curve according to the curing age was traced to analyse the variation patterns. Finally, a specific equation to estimate the curing strength without destructive test was derived using regression analysis based on the wave velocity hysteresis and the results from the compression test.     

Long-term strength and durability parameters of lightweight concrete in hot regime: importance of initial curing

The paper presents results on strength development and durability of 35 and 50 MPa total lightweight concretes exposed to hot marine exposure conditions for a period of 7 years. An initial water curing of 7 days and subsequent seaside exposure was found more beneficial for the strength development of lightweight concrete. One day of initial curing and subsequent seaside exposure was not very conducive for the strength development. A marginal degradation in both the stiffness and the modulus of rupture of the concretes over the exposure period was observed. Likewise, the water penetrability of the two mixtures, for all the three initial curing regimes, increased over a period of 7 years. This establishes that the compressive strength of concrete is not synonymous with its durability. Overall, 3–7 days of initial water curing seems most desirable to enhance the durability of concrete exposed to hot salty marine exposure conditions.     

混凝土内养护技术研究进展

高强混凝土水胶比低、渗透性差,外部养护水难以进入混凝土内部,造成传统外部养护效果变差,由此产生的自收缩会导致材料的开裂敏感性提高.通过在混凝土配合比中引入高吸水性材料来实现内养护是解决此问题的有效途径.综述了目前混凝土常用的内养护材料及其物理力学特征和用量,阐述了混凝土内养护理论基础、自收缩产生机理和内养护减缩机制,总结了不同内养护材料对减少混凝土收缩和影响力学性能的规律：一般来说,内养护可以减少自收缩,但对干燥收缩的影响与引入水量有关,对混凝土强度和弹性模量则会产生不利影响.最后,提出了当前混凝土内养护技术研究存在的问题及未来可能的研究方向.     

Multiple linear regression,artificial neural network,and fuzzy logic prediction of 28 days compressive strength of concrete

Evaluating the in situ concrete compressive strength by means of cores cut from hardened concrete is acknowledged as the most ordinary method, however, it is very difficult to predict the compressive strength of concrete since it is affected by many factors such as different mix designs, methods of mixing, curing conditions, compaction, etc. In this paper, considering the experimental results, three different models of multiple linear regression model (MLR), artificial neural network (ANN), and adaptive neuro-fuzzy inference system (ANFIS) are established, trained, and tested within the Matlab programming environment for predicting the 28 days compressive strength of concrete with 173 different mix designs. Finally, these three models are compared with each other and resulted in the fact that ANN and ANFIS models enables us to reliably evaluate the compressive strength of concrete with different mix designs, however, multiple linear regression model is not feasible enough in this area because of nonlinear relationship between the concrete mix parameters. Finally, the sensitivity analysis (SA) for two different sets of parameters on the concrete compressive strength prediction are carried out.     

“类干热”养护法快速推定预拌混凝土强度的试验探索

该文结合混凝土搅拌站"人、机、料、法、环"五因素现状,在干热养护和湿热养护基础上探索一种新的养护方式——"类干热"养护,试验结果表明采用"类干热"养护法可快速推定混凝土强度,为预拌混凝土生产质量控制环节提供良好手段。