既有建筑混凝土强度按批评定的研究及探讨

既有建筑结构检测鉴定中确定混凝土强度的因素复杂,混凝土构件强度多数不能全数检测,标准差未知的抽样检测按检测批评定时应按要求确定混凝土强度的推定区间。现行规范对检测既有建筑混凝土强度的构件测区数目的要求不一定适用,按现行规范的统计方法给出的下限值不能包住总体中的某些数值,有时甚至低于下限值较多。因此,建议以能评定单个构件推定值的测区数为原则,更广泛地选取构件测区作为样本;对包含样本下侧值的构件应按现行规范评定其单个构件的推定值,并进行异常性判断。下限值的取值建议应综合考虑现行规范及样本空间中包含下侧数值构件的混凝土强度推定值。     

混凝土强度推定区间的理解与应用

在工程质量验收和结构性能评定中,往往需要确定结构实体中混凝土强度,现行规范中要求给出混凝土强度推定区间。但是检测人员在运用时往往出现理解上的偏差。通过理论分析和工程应用,进一步阐述了推定区间的概念和抽样检测混凝土强度的置信区间的表达方式,并分析了不同生产方风险和使用方风险下的推定区间的差异。     

基于置信度议混凝土强度批量检测

在对混凝土强度进行批量检测时,需根据样本的平均值、标准差推定检验批的混凝土强度。国家现行规范有三种方法推定混凝土强度:①计算推定区间,并以推定区间的上限值作为混凝土强度推定值;②计算推定区间,并根据实际情况在推定区间取值;③用样本平均值减去1.645倍标准差作为推定值。本文通过分析三种方法的计算的理论依据,发现以推定区间上限值作为批量评定值会导致评定结果偏大,根据实际情况在推定区间取值随意性较大;用样本均值减去1.645倍标准差作为推定值不准确。本文建议用样本平均值减去k倍样本标准差,k值取为置信度γ=0.5所对应的单侧规范限k系数。     

混凝土强度检验评定实践的主要问题与建议

混凝土强度是混凝土结构安全性的重要指标。当前,混凝土强度检验评定实践存在混凝土试件的代表性和真实性受质疑、检测报告存在诱导性错误、将较小强度值的试件剔除后再评定检验批混凝土强度、检测推定无效试件代表的结构实体强度及将回弹法作为验收标准等问题。以某地工程建设实际为例,从实证方面分析并讨论了上述问题,最后从建设工程质量政府监管角度提出相应的建议。     

关于CECS03:2007中单个构件混凝土强度推定值的讨论

用有效芯祥试件混凝土的抗压强度值中的最小值确定单个构件混凝土强度推定值,其结果偏低,建议用芯样平均值或中间值作为单个构件混凝土抗压强度推定值,建议用芯样强度推定值不小于规定抗压强度的0.85倍,芯样最小值不小于规定抗压强度的0.75倍作为单个构件混凝土抗压强度混凝土合格评定标准。     

建筑工程主体结构混凝土强度实体检验探析

工程质量问题的关注度日益增加,反映主体结构安全性的实体检测在工程主体验收时愈发重要。各类混凝土建筑实体检测项目重点是混凝土强度的检测,强度检测的数据是工程质量验收的必要支撑。文章结合实际工程对混凝土结构实体检测中混凝土强度项目进行了检测实施,分析了规范的检测抽样原则,进行了基本受力构件楼板及梁柱混凝土强度的同条件试块法与回弹-取芯综合法的检测实施,指出了实体检测中的盲、难点的处理措施,为实体检测工作起到一定的参考作用,可供类似工程项目的检测借鉴。     

强化施工现场混凝土质量的控制及验收

通过震害调查分析指出,混凝土结构的实体强度很难用灾后检测的推定强度测准,也难以用标养强度反映.基于工程实践提出的用同条件养护试件验收实体强度的方法能够比较好地反映实际结构性能,满足设计目标.经过近年系统的试验研究,同条件强度验收的方法己渐趋完善,能够促进施工现场加强量控制,保证工程质量.     

建筑鉴定中混凝土抗压强度推定方法的探讨

从构件抽检数量、混凝土强度推定公式及构件检测结果真实性判别等方面,分析了<回弹法检测混凝土抗压强度技术规程>、<建筑结构检测技术标准>和<民用建筑可靠性鉴定标准>中关于混凝土构件强度推定的规定和计算方法,认为<建筑结构检测技术标准>对于混凝土强度推定值是否合格有一个较明确的结论,并通过算例分析表明,<建筑结构检测技术标准>在检测数量上更为灵活,但其检测结果会比其它规范计算得出的值要高.由于规范对于强度推定真实性的判别方法不一样,得出结果也会不一样.     

建筑鉴定中混凝土抗压强度推定方法的探讨

从构件抽检数量、混凝土强度推定公式及构件检测结果真实性判别等方面,分析了《回弹法检测混凝土抗压强度技术规程》、《建筑结构检测技术标准》和《民用建筑可靠性鉴定标准》中关于混凝土构件强度推定的规定和计算方法,认为《建筑结构检测技术标准》对于混凝土强度推定值是否合格有一个较明确的结论,并通过算例分析表明,《建筑结构检测技术标准》在检测数量上更为灵活,但其检测结果会比其它规范计算得出的值要高。由于规范对于强度推定真实性的判别方法不一样,得出结果也会不一样。     

混凝土抗压强度批量检测推定值的讨论

针对钻芯法混凝土抗压强度批量检测时,推定区间不满足限值要求的推定值问题,基于混凝土抗压强度的正态分布特性,从错判概率和漏判概率的角度重点分析最小值大于设计值时,最小值作为推定值的适宜性问题。结论为当最小值小于推定区间下限或在区间内时可以作为推定值;当最小值大于推定区间上限时不宜作为推定值。该结论对钻芯法混凝土批量检测有较好的指导作用。     

水泥石对废混凝土蒸压试样强度的影响

模拟废混凝土进行蒸压处理,研究了水泥石对蒸压试样强度的影响.结果表明,水泥石的存在显著提高了蒸压试样的强度.当水泥石量较少(＜12.5%)时,其蒸压试样强度随着水泥石量的增加而增加;水泥石量＞12.5%以后,其蒸压试样强度随着水泥石量的增加没有明显变化.由于普通混凝土的水泥用量按水化水泥量计算均超过12.5%,普通混凝土磨细制成蒸压试样的强度受废混凝土中水泥石量的影响很小.     

A preliminary concrete mix design for SCC with marble powders

The marble has been commonly used as a building material since ancient times. Disposal of the waste materials of the marble industry, consisting of very fine powders, is one of the environmental problems worldwide today. However, these waste materials can be successfully and economically utilized to improve some properties of fresh and hardened self-compacting concrete (SCC).The aim of this study is to find some relationship between properties of the fresh SCC and the hardened SCC containing marble powder. For this purpose, the mix design approach based on monogram developed by Monteiro and co-workers for normal vibrated concrete was adapted to SCC mixes. In order to obtain this monogram, a series of SCC mixes with different water/cement ratios and water/powder ratios were prepared. Several tests such as slump-flow, T₅₀₀ time, L-box, V-funnel and sieve segregation resistance were applied for fresh concrete and tests such as compressive strength and split-tension strength at 7, 28 and 90 days were performed for hardened concrete. In conclusion, the mix design method based on monogram can be suggested for preliminary design in SCC.     

钻孔取芯—测试硬化砼强度的好手段

采用钻取芯样测试砼强度，简便快捷、精度高、可信度大，是目前检测硬化砼强度的好方法。     

引气剂液膜单分子层及硬化混凝土气孔结构分析

利用膜天平研究了两种引气剂GYQ和改性松香R在空气-水界面的液膜单分子层强度,采用光学显微镜测孔法分析了硬化引气混凝土的气孔结构,并考察了高频振捣对掺2种引气剂的混凝土气孔结构的影响。结果表明,引气剂在空气-水界面上的单分子膜强度是影响引气剂稳泡性能的重要参数之一。掺加稳泡性能优异的高性能引气剂,可以在混凝土中引入更加细小、稳定、分布合理的气泡,硬化混凝土具有更优化的气孔结构。高频振捣破坏了混凝土中的大直径气泡,合理的振捣时间优化了混凝土的气孔结构。     

掺合料裹骨料工艺对再生骨料混凝土性能的影响

采用一种掺合料裹骨料搅拌工艺,在水泥裹骨料工艺基础上,进一步改善再生骨料-水泥石界面过渡区,提高再生混凝土性能,研究了搅拌工艺、新拌混凝土坍落度、掺合料品种对再生混凝土强度和抗氯离子渗透性的影响.结果表明,采用掺合料裹骨料工艺,可在水泥裹骨料工艺基础上进一步大幅度提高早龄期强度和抗氯离子渗透性能,对后期强度和抗氯离子渗透性也有提高,但幅度较小;提高新拌混凝土坍落度有助于提高强度,但对抗氯离子渗透性能略有影响,采用掺合料裹骨料工艺可减小坍落度对再生混凝土性能的影响;采用矿渣掺合料更有助于提高再生混凝土强度和抗氯离子渗透性能.     

Self-compacting concrete with different levels of pulverized fuel ash

This research investigated self-compacting concrete (SCC) with levels of up to 80% cement replacement by fly ash in mixes adjusted to give constant fresh concrete properties. The hardened concrete and the relationships between hardened properties were then studied.The results show that SCC with up 80% cement replaced by fly ash is possible. To keep the filling ability constant, replacement of cement with fly ash would require an increase in water/powder (W/P) ratio and a reduction in superplasticiser dosage. They also show fly ash have negative effects on passing ability, consistence retention and hardened concrete properties such as strength. The comparison between SCC and normally vibrated concrete (NVC) shows that their material properties of are similar. The successful completion of this project can lead to the use of higher volume fly ash in SCC.     

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.     

Mechanical properties of hybrid fiber reinforced lightweight aggregate concrete made with natural pumice

The purpose of this study is to improve the ductility of pumice lightweight aggregate concrete by incorporating hybrid steel and polypropylene fibers. The changes in mechanical properties and also bulk density and workability of pumice lightweight aggregate concrete due to the addition of hybrid steel and polypropylene fibers have been studied. The properties were investigated include bulk density and workability of fresh concrete as well as compressive strength, flexural tensile strength, splitting tensile strength and toughness of hardened concrete. Nine concrete mixtures with different volume fractions of steel and polypropylene fibers were tested. A large increase in compressive and flexural ductility and energy absorption capacity due to the addition of steel fibers was observed. Polypropylene fibers, on the other hand, caused a minor change in mechanical properties of hardened concrete especially in the mixtures made with both steel and polypropylene fibers. These observations provide insight into the benefits of different fiber reinforcement systems to the mechanical performance of pumice lightweight aggregate concrete which is considered to be brittle. These results provide guidance for design of concrete materials with reduced density and enhanced ductility for different applications, including construction of high-rise, earthquake-resistant buildings.     

大流动性再生粗集料混凝土配合比设计方法

采用相同砂浆体积(EMV)方法配制再生粗集料混凝土,可节省水泥及细集料的用量,其强度及弹性模量与对比天然集料混凝土(NAC)相近,但由于新拌砂浆含量小而使其流动性能变差.给出了EMV方法的改进方法及具体设计步骤,并应用该改进方法配制2种不同来源再生粗集料的大流动性再生粗集料混凝土(FRAC),测定其坍落度、干湿表观密度、立方体抗压强度、轴心抗压强度、劈裂抗拉强度以及弹性模量.结果表明:采用改进EMV方法可配制出满足和易性要求的FRAC,而且与传统方法配制的FRAC相比,其各项性能指标更接近对比NAC.     

新型阻锈剂对钢筋混凝土阻锈作用的研究（Ⅱ）：对砂浆／钢筋界面特性和砂浆性能的影响

用XPS研究了新型阻锈剂DETA-TU在钢筋混凝土中的分布及其对水泥水化作用、新拌砂浆的流动性、硬化砂浆的强度和抗氯离子渗透性的影响,结果表明,DETA-TU能够富集在混凝土/钢筋界面,这对提高DETA-TU的阻锈效果是有益的,DETA-TU对水泥水化有一定的延缓作用,同时又可改善水泥砂浆的流动性,但砂浆的28d强度有所下降,它还能显著提高砂浆的抗氯离子渗透性。