Experimental study on the compressive strength of grouted concrete block masonry based on nondestructive detection methods

Existing nondestructive detection methods were adopted to test the compressive strength of grouted concrete block masonry,i.e.the rebound method,pulling-out method and core drilling method were employed to test the strength of block,mortar and grouted concrete,respectively.The suitability of these methods for the testing of strength of grouted concrete block masonry was discussed,and the comprehensive strength of block masonry was appraised by combining existing nondestructive or micro-destructive detection methods.The nondestructive detection test on 25 grouted concrete block masonry specimens was carried out.Experimental results show that these methods mentioned above are applicable for the strength detection of grouted concrete block masonry.Moreover,the formulas of compressive strength,detection methods and proposals are given as well.

Application of Geological Prospecting Radar to Detecting the Reinforced Concrete Blocks of East Runway of the Capital International Airport of China

The geological prospecting radar, a high-techuology rapidly developed in recent years, is used in the field of nondestructive testing and object detecting, in accordance with the reflection principle of high-frequency electromagnetic wave. It will be effective if there exists a large difference in the electromagnetic properties between an object body and its surroundings. The result of using the geological prospecting radar in detecting the concrete blocks with ber in the capital internatioual airport’s east runway is aualyed in detail herein. The introduction of the geological prospecting radar provides a new approach to nondotodive testing.

Quality Assessment of Concrete Blocks Exposed in Nature for Eighty Years

The concrete blocks used on a jetty in Shanghai were made in 1909 and 1910. Having been exposed in nature for 80 years, now there are 4600 pieces of blocks left on the jetty. Comprehensive inspections, such as external appearance examination, core-drilling of concrete blocks, ultrasonic detection, nuclear densimeter inspection and in-door and out-door chemical analysis, show that 75% of the blocks are of the rebound number of 21 - 23, and the saturated limit compressive strength and dry limit compressive strength of 10MPa; the carbonized depth of concrete is 1 - 2 mm. Compared with the state of the jetty in 1968, already used for 60 years then, the jetty is expected to serve another 40 years or more after being repaired.

Experimental Performance Measures of Recycled Insulation Concrete Blocks from Construction and Demolition Waste

Construction and demolition(C&D)waste has seriously affected the ecological environment.The utilization of C&D waste resources can greatly alleviate this problem,and it is an important way to help achieve the goal of zero carbon in 2050.In this study,insulation concrete blocks were developed with recycled aggregates,cement,fly ash as main raw materials,expanded polystyrene(EPS)insulation boards as block insulation filling material,and selfdeveloped construction waste composite activator,interface enhancer,surface modifier and other additives.Through experimental research and performance test analysis,the best mix ratio of the product and the mechanism of each additive were proved.The experimental results showed that the insulation concrete block prepared under the conditions of recycled aggregates sand ratio of 45%,active activator Na_(2)SO_(4)content of 0.15%and fly ash content of 30%has the best performance and meets the relevant standards.

Mechanical Behavior of Concrete Block Masonry

The main objective of this study is to verify, through compression tests on different prisms, the vertical and horizontal deformability and the failure modes of the components of concrete blocks under compression. In this study two mortar mixes were tested, along with two types of prism, with and without the presence of a vertical joint. The conclusions were： the appearance of non-linearities of the masonry corresponds to an increase in the lateral strain due to extensive cracking of the material and a progressive increase in the Poisson ratio, the cracks in the three-block prisms built with the mortar type I were vertical, occurring symmetrically on both sides; the prisms built with mortar type II had, as a consequence of localized crushing, an association with vertical cracks due to the concentrations of stresses at some points, the presence of a vertical joint led to the appearance of separation cracks between the middle block and the vertical mortar joint, when the stress reached approximately 30% of the compressive strength of the set; the prisms with two whole blocks and one vertical joint （B） built with the mortars of mixes I and II had a compressive strength of the order of 42% and 66% of the prisms with three whole blocks （A）, respectively.

Research on Concrete Beam Crack Recognition Algorithm Based on Block Threshold Value Image Processing

To solve the problem that the digital image recognition accuracy of concrete structure cracks is not high under the condition of uneven ill umination and complex surface color of concrete structure,this paper has proposed a block segmentation method of maximum entropy threshold based on the digital image data obtained by the ACTIS automatic detection system.The steps in this research are as follows:1.The crack digital images of concrete specimens with typical fea-tures were collected by using the Actis system of KURABO Co,Ltd,of Japan in the concrete beam bending test.2.The images are segmented into blocks to dis-tinguish backgrounds of different grayscale.3.The max imum interclass average gray difference method is used to distinguish the sub-blocks and screen out the image blocks that need to be segmented.4.Segmentation is made to the image with 2D max imum entropy threshold segmentation method to obtain the binary image,and the target image can be obtained by screening the connected domain features of the binary image.Results have shown that compared with other algo-rithms,the proposed method can effectively decrease the image over-segmentation and under segmentation rates,highlight the characteristics of the target cracks,solve the problems of excessive difference between the identified length and actual length of cracks caused by background gray level change and uneven ilumnination,and effectively improve the recognition accuracy of bridge concrete cracks.

Analysis of Waste in the Production of Concrete Blocks---A Case Study in the Goias Industry

An ever more demanding consumer market and the need for companies to be more competitive have led organizations to try to eliminate waste. This research is a case study which presents a proposal for intervention in order to improve performance of a pre-cast concrete block factory in outer Goihnia. As a first step, waste in the production process was identified through analysis of data on time involved in each step of the process. Then, applying the concepts of lean production, a list of activities was drawn up with a view to eliminating non-value-added work, identifying waste, decreasing cycle time, streamlining the production process and increasing the flexibility and transparency of the process. From the results, it was possible to identify the sources of waste and provide management with information for strategic decisions about production. Finally, various suggestions were made with a view to eliminating or mitigating bottlenecks in the production process.

Autoclaved Aerated Concrete Block Prefabricated Multi-Storey Building Technology

In active response to the national requirements of promoting green building materials and developing prefabricated buildings,it is necessary to continuously optimize and reasonably employ relevant technologies.Autoclaved aerated concrete block prefabricated multi-storey building technology is a new technology,which will not only effectively realize green environmental protection in construction engineering,but also promote the further development of prefabricated buildings.Therefore,this paper analyzes the autoclaved aerated concrete block prefabricated multi-storey building technology for future references.

Studying the Properties of Lightweight Concrete Using Construction Materials Waste

The main purpose of this research is to study the mechanical properties of lightweight concrete through the using of different types of lightweight aggregate. Three types of lightweight aggregate were used in this study for the production of lightweight concrete. These types are red block aggregate, red ceramic aggregate and white thermostone aggregate. All these types have been brought from construction waste. A comparison of the properties of lightweight concrete with normal concrete is the most important goal of this study. The most important properties of concrete, which were compared with each other is compressive strength, static modulus of elasticity, splitting tensile strength and slump flow.

Thermal Analysis of Concrete Mixtures with Recycled EPS Aggregates

Reusing recycled waste materials in buildings is gaining more and more attention for what it offers economic,environmental,and energy benefits;and many researchers are nowadays working on producing new sustainable construction materials incorporating recycled wastes.In this scope,this work uses an experimental approach aiming at understanding the effect of incorporating Expanded Polystyrene(EPS)beads in concrete and proposing thermally improved concrete mixtures for the production of hollow blocks in Lebanese constructions by substituting fine aggregates with recycled products such as EPS in order to promote their insulating properties.Three different diameters of EPS beads(2 mm~3 mm,3 mm~4 mm and 4 mm~5 mm)are studied with different volumetric ratios(20%,40%,60%and 80%)in order to investigate the effect of EPS on the thermal properties of concrete.The results showed that the only the percentage of incorporated EPS beads impacted the thermal performance of the concrete mixtures while the EPS diameters have a negligible effect on the thermal properties of the concrete samples.

钢管混凝土双块式轨枕无砟轨道结构疲劳性能试验研究

新型钢管混凝土(CFT)双块式轨枕克服了桁架钢筋双块式轨枕存在的生产制造复杂、存放易锈蚀、运营阶段易开裂等问题,可广泛应用于高速铁路和城市轨道交通无砟轨道结构。为检验CFT双块式轨枕无砟轨道结构的疲劳性能,采用11根预制CFT双块式轨枕现浇制作足尺无砟轨道结构节段模型,开展橡胶隔振垫式减振轨道和现浇整体式轨道节段的疲劳试验,揭示其疲劳损伤特性,分析典型疲劳加载循环次数后静载作用下轨道结构应变和变形分布及其演化规律。研究结果表明:1.5倍静轴重的疲劳荷载累计作用500万次后,减振节段及整浇节段CFT双块式轨枕无砟轨道结构混凝土均未出现肉眼可见的裂缝,轨枕与现浇道床整体工作性能良好,疲劳性能满足规范要求;停机开展静载试验过程中轨道结构各测点混凝土横向应变值随荷载增大而近似线性增大,最大拉压应变值均远小于混凝土的极限应变值,工作状态良好;轨道整浇节段道床板中处于整体受拉的状态,可见设置层间连接钢筋实现了道床与底座的共同工作;疲劳试验过程中轨道结构测点竖向位移值总体随着静载的增大而逐渐增大,位移量级较小,满足规范要求,减振轨道节段竖向位移值及其变化率大于整浇轨道节段。研究结果可供类似研究及钢管混凝土双块式轨枕无砟轨道结构工程应用参考。

废水泥浆对陶粒加气混凝土砌块性能的影响研究

在废水泥浆中的水取代全部拌合水的条件下,探究废水泥浆中的粉体以等量取代或系数为0.65~1.05折算取代部分粉煤灰时,对陶粒加气混凝土和易性及陶粒加气混凝土砌块抗压强度、干密度、干燥收缩、导热系数的影响。研究表明,水胶比为0.45,当废水泥浆浓度为0~18%时,按等量取代后,砌块28 d平均抗压强度为5.51~5.54 MPa,干密度为728~730 kg/m~3,干燥收缩值为0.28~0.41 mm/m,导热系数为0.137~0.145 W/(m·K);当废水泥浆浓度为20%时,按系数为0.75~0.95折算取代后,砌块28 d平均抗压强度为5.18~5.43MPa,干密度为732~743 kg/m~3,干燥收缩值为0.35~0.42 mm/m,导热系数为0.146~0.178 W/(m·K),此时,砌块符合JG/T 504—2016对CA5.0B07砌块要求。

沿海地区台风荷载下陶粒加气混凝土砌块填充墙斜裂缝试验研究

为研究沿海地区低抗震设防烈度条件下陶粒加气混凝土砌块填充墙的开裂原因,采用PKPM软件分析了某13层框架结构住宅在台风荷载和6度抗震设防烈度下结构的层间位移,结果表明:在该地区基本风压下,该工程的最大层间位移角与6度抗震设防烈度时基本相当。同时进行了一榀足尺框架模型试验,结果表明,当主体结构还在弹性阶段时,模型的整体刚度就急剧下降,填充墙就已经开裂。当试件的位移角达到1/1 092时,填充墙开裂严重,此时相当于刚度修正后的13层框架住宅案例在1.27kN/m^(2)的风压下的表现。因此按照目前的结构设计参数取值和施工构造措施,沿海地区陶粒加气混凝土砌块填充墙的开裂在所难免。为避免该斜裂缝发生,应在设计和施工阶段采取新的设计方法和构造措施。

新型钢管混凝土枕式无砟轨道动力响应试验研究

采用钢管混凝土构件连接轨枕块形成钢管混凝土轨枕,基于钢管混凝土轨枕设计城市轨道交通用钢管混凝土枕式无砟轨道结构。为掌握钢管混凝土枕式无砟轨道结构在城市轨道交通列车运行条件下的力学性能,验证结构设计的安全性、合理性,分别在减振地段、普通地段铺设钢管混凝土枕式无砟轨道,通过行车试验,测试分析不同列车行驶速度下无砟轨道钢轨、轨枕、道床结构的动力响应。研究结果表明:在列车车速为40、60和80 km/h运行条件下,轮轨垂向力最大值为86.18 kN,横向力最大值为13.99 kN,脱轨系数最大值为0.21,轮重减载率最大值为0.23,测试值均明显小于相应的安全限值,无砟轨道结构满足行车安全性要求;在列车动荷载作用下,钢管混凝土轨枕钢管压应力最大值为3.55 MPa,拉应力最大值为3.77 MPa;轨枕块压应力最大值为1.32 MPa;道床钢筋压应力最大值为2.30 MPa,拉应力最大值为3.54 MPa;道床底压应力最大值0.22 MPa。这些动力响应结果均满足材料的的限值,表明结构保持了良好的力学性能,结构设计合理可行。

马鞍山长江公铁大桥主航道桥中塔下横梁施工关键技术

马鞍山长江公铁大桥主航道桥Z4号中塔采用空间四肢A形钢-混组合塔,横向两塔肢间设下横梁,下横梁间设3道系梁,纵向两塔肢间不设置横梁。下横梁采用支架法分层浇筑施工。下横梁施工支架采用落地式钢管支架配套模板体系,受力性能满足要求;通过有限元计算比选下横梁混凝土分层浇筑方案并进行优化,采取(5.5+2.5)m分层方案,上、下层混凝土分别分为2块、3块分层分块浇筑;通过低温升、易泵送、高抗裂的C60混凝土研制、下横梁与塔柱倒弧结合面抗裂措施优化、分块间接缝构造形式及施工工艺优化、下横梁与系梁混凝土浇筑施工组织优化、混凝土温度智能化监控、预应力束张拉时机控制等混凝土防裂措施,有效解决了下横梁大体积混凝土易开裂的难题。

生活垃圾焚烧灰渣的预处理和理化性质研究

为了加大生活垃圾焚烧灰渣的资源化利用,对其预处理工艺和理化性质进行了试验研究。通过采用分选、除盐、干燥和筛分等预处理工艺,将灰渣筛分出粒径>0.15 mm的颗粒状灰渣和粒径≤0.15 mm的粉状灰渣;然后依次进行灰渣的放射性、重金属浸出的安全性指标检测,微观形貌、表观密度和吸水率等物理性质试验,化学元素、矿物组成、酸碱度和活性指标等化学性质分析。研究发现,灰渣的安全性达到相关标准,颗粒状灰渣和粉状灰渣分别与陶砂和粉煤灰的理化性质相近。利用生活垃圾焚烧灰渣开发生产陶粒加气混凝土砌块在理论上可行,由此可以探索一种生活垃圾焚烧灰渣资源化利用的新途径。

MU10再生混凝土承重砌块力学性能与抗冻性试验研究

为进一步提高废弃混凝土利用率,促进严寒地区应用再生混凝土承重砌块,在分析再生骨料物理性能的基础上,考虑了100%再生粗骨料取代率、水胶比、用水量及粉煤灰掺量的影响,采用正交试验设计了C30再生混凝土配合比来制备MU10再生混凝土承重砌块,通过分析MU10再生混凝土承重砌块的力学性能,确定了MU10再生混凝土承重砌块的最佳配合比,利用环境模拟箱验证了MU10再生混凝土承重砌块的抗冻性。结果表明:再生骨料与天然骨料相比表面较粗糙,附着部分旧水泥砂浆,具有低密度,高孔隙率、吸水率和含泥量,压碎指标是天然骨料的两倍左右;MU10再生混凝土承重砌块的最佳配合比为再生粗骨料1 172 kg/m^(3)、天然河砂578 kg/m^(3)、水泥400 kg/m^(3)、粉煤灰100 kg/m^(3)、水150 kg/m^(3),其抗压强度为11.4 MPa,抗折强度为2.1 MPa,可用于承重及有抗震要求的砌体结构;经过50次冻融循环后,MU10再生混凝土承重砌块的质量损失为1.2%、强度损失为18.1%,抗冻性能符合要求,可以作为严寒地区新型墙体材料使用。

灌孔配筋混凝土模壳砌块基础竖向承载性能试验研究与分析

灌孔配筋混凝土模壳砌块基础具有免支模、整体性好、易施工等优点,为了研究其竖向承载性能和失效破坏模式,通过试验和数值分析研究了配筋方式、试件高度、侧向土压力等因素的影响。结果表明:模壳砌块参与灌孔配筋混凝土模壳砌块基础受力,其在失效破坏时外围剥落、内部横肋可被灌孔混凝土有效约束;内置箍筋能显著提高试件开裂荷载并改善变形性能,但对竖向极限承载力无显著影响,失效时箍筋呈受压屈曲灯笼状外鼓;试件高度增加即高厚比增加,竖向极限承载力小幅下降(最大降幅5.35%);侧向土压力对无箍筋试验组的竖向承载性能无显著影响,但其与内置箍筋会形成双重约束作用并显著改善内置箍筋基础的竖向承载性能。GB/T 50003—2011《砌体结构设计规范》适用于灌孔配筋混凝土模壳砌块基础竖向极限承载力的计算,建立的有限元模型分析结果可靠,可为工程应用或同类研究提供参考。

圆钢管再生镍铁渣混凝土柱冲击性能试验

为研究掺镍铁渣钢管再生混凝土柱抗冲击性能,以粗骨料替代率、轴压比、落锤质量及冲击能量为变化参数,设计并制作了11根圆钢管再生混凝土柱。通过落锤冲击试验,得到了试件的破坏形态、位移时程曲线及冲击力时程曲线,研究了轴压比、粗骨料取代率、冲击能量和落锤质量对钢管再生混凝土柱侧向冲击性能的影响。结果表明:钢管再生混凝土柱抗冲击性能良好,能量吸收率基本恒定在67%左右;与取代率为0%相比,再生粗骨料取代率为30%时,试件跨中挠度平均降低8.9%;再生粗骨料取代率为70%时,试件跨中挠度平均降低11.4%;随着冲击能量的增加,试件跨中残余位移显著增大;轴压比在0~0.4以内,轴向力对钢管再生混凝土抗冲击性能有提高作用;落锤质量由330 kg增加至430 kg,冲击持续时间增加16%;套箍系数增大,跨中挠度减小。

基于数值模拟的混凝土联排水动力特性研究

海上风电桩基础冲刷坑的存在对风电场安全运行造成不利影响,须采用有效的冲刷防护措施稳固桩周泥沙。该文以山东海域某海上风电场为研究对象,提出混凝土联锁排防护措施,并将其简化为六列矩形块阵列模型,通过数值模拟分析了矩形块阵列模型的水动力特性。研究发现,第1排矩形块为整个矩形阵列模型的主要受力块,混凝土联锁排整体阻力可通过单独计算第1排单个矩形块来评估,能显著减少计算量;其次,矩形块阻力系数随时间变化具有周期性,但随时间变化幅度较小。总体而言,本文结果对指导混凝土连锁排防护设计具有一定的工程意义。