Simulation of Fracture Process of Lightweight Aggregate Concrete Based on Digital Image Processing Technology

The mechanical properties and failure mechanism of lightweight aggregate concrete(LWAC)is a hot topic in the engineering field,and the relationship between its microstructure and macroscopic mechanical properties is also a frontier research topic in the academic field.In this study,the image processing technology is used to establish a micro-structure model of lightweight aggregate concrete.Through the information extraction and processing of the section image of actual light aggregate concrete specimens,the mesostructural model of light aggregate concrete with real aggregate characteristics is established.The numerical simulation of uniaxial tensile test,uniaxial compression test and three-point bending test of lightweight aggregate concrete are carried out using a new finite element method-the base force element method respectively.Firstly,the image processing technology is used to produce beam specimens,uniaxial compression specimens and uniaxial tensile specimens of light aggregate concrete,which can better simulate the aggregate shape and random distribution of real light aggregate concrete.Secondly,the three-point bending test is numerically simulated.Thirdly,the uniaxial compression specimen generated by image processing technology is numerically simulated.Fourth,the uniaxial tensile specimen generated by image processing technology is numerically simulated.The mechanical behavior and damage mode of the specimen during loading were analyzed.The results of numerical simulation are compared and analyzed with those of relevant experiments.The feasibility and correctness of the micromodel established in this study for analyzing the micromechanics of lightweight aggregate concrete materials are verified.Image processing technology has a broad application prospect in the field of concrete mesoscopic damage analysis.

The Testing Strength Curves of Lightweight Aggregate Concrete by Rebound Method and Ultrasonic-rebound Combined Method

The strength curves of lightweight aggregate concrete （LWAC） were tested based on detecting LWAC with density of 1 400-1 900 kg/m3 and LWAC with strength grade of LC15-LC50 by rebound method and ultrasonic-rebound combined method.The results show that the common measured strength curves tested by above two methods can not satisfy the required accuracy of LWAC strength test.In addition,specified compressive strength curves of testing LWAC by rebound method and ultrasonic-rebound combined method are obtained,respectively.

Autogenous Shrinkage of High Strength Lightweight Aggregate Concrete

The characteristic of autogenous shrinkage（AS） and its effect on high strength lightweight aggregate concrete（HSLAC） were studied.The experimental results show that the main shrinkage of high strength concrete is AS and the amount of cement can affect the AS of HSLAC remarkably,At the early stage the AS of HSLAC is lower than that of high strength normal concrete,but it has a large growth at the later stage.The AS of high strength normal concrete becomes stable at 90d age,but HSLAC still has a high AS growth .It is found that adjusting the volume rate of lightweight aggregate,mixing with a proper dosage of fly ash and raising the water saturation degree of lightweight aggregate can markedly reduce the AS rate of HSLAC.

Influence Mechanism of Curing Regimes on Interfacial Transition Zone of Lightweight Ultra-High Performance Concrete

This study aims to clarify the effects of curing regimes and lightweight aggregate(LWA)on the morphology, width and mechanical properties of the interfacial transition zone(ITZ) of ultra-high performance concrete(UHPC), and provide reference for the selection of lightweight ultra-high performance concrete(L-UHPC) curing regimes and the pre-wetting degree LWA. The results show that, under the three curing regimes(standard curing, steam curing and autoclaved curing), LWA is tightly bound to the matrix without obvious boundaries. ITZ width increases with the water absorption of LWA and decreases with increasing curing temperature. The ITZ microhardness is the highest when water absorption is 3%, and the microhardness value is more stable with the distance from LWA. Steam and autoclaved curing increase ITZ microhardness compared to standard curing. As LWA pre-wetting and curing temperatures increase, the degree of hydration at the ITZ increases, generating high-density CSH(HD CSH) and ultra-high-density CSH(UHD CSH), and reducing unhydrated particles in ITZ. ITZ micro-mechanical properties are optimized due to hydration products being denser.

Influence of Polymer Addition on Performance and Mechanical Properties of Lightweight Aggregate Concrete

The influence of polymer addition on microstructure, performance and mechanical properties of lightweight aggregate concrete was investigated. It was found that the addition of polymer improved the performance and mechanical properties of lightweight aggregate concrete. It was ascertained that the modification of microstructural uniformity and densification with the addition of polymer is responsible for the enhancement of mechanical properties. With respect to compressive strength and bending strength, the lightweight aggregate concrete added with 13% ethylene-acetate ethylene interpolymer (EVA) exhibits preferred mechanical properties. Key words lightweight aggregate concrete - polymer - microstructure - mechanical properties CLC number TU 528.2 Foundation item: Supported by the National Nature Science Foundation of China (50272045)Biography: Jiang Cong-sheng (1963-), male, Ph. D candidate, Associate professor, research direction: advanced architectural materials.

Engineering properties of sintered waste sludge as lightweight aggregate in a densified concrete mixture

The global trend towards carbon reduction,energy conservation,and sustainable use of resources has led to an increased focus on the use of waste sludge in construction.We used waste sludge from a reservoir to produce high-strength sintered lightweight aggregate,and then used the densified mixture design algorithm to create high-performance concrete from the sintered aggregate with only small amounts of mixing water and cement.Ultrasonic,electrical resistance and concrete strength efficiency tests were perfo...

Evaluation method of cracking resistance of lightweight aggregate concrete

The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.

Preparation and properties of geopolymer-lightweight aggregate refractory concrete

Geopolymer-lightweight aggregate refractory concrete (GLARC) was prepared with geopolymer and lightweight aggregate. The mechanical property and heat-resistance (950 ℃) of GLARC were investigated. The effects of size of aggregate and mass ratio of geopolymer to aggregate on mechanical and thermal properties were also studied. The results show that the highest compressive strength of the heated refractory concrete is 43.3 MPa,and the strength loss is only 42%. The mechanical property and heat-resistance are influenced by the thickness of geopolymer covered with aggregate,which can be expressed as the quantity of geopolymer on per surface area of aggregate. In order to show the relationship between the thickness of geopolymer covered with aggregate and the thermal property of concrete,equal thickness model is presented,which provides a reference for the mix design of GLARC. For the haydite sand with size of 1.18-4.75 mm,the best amount of geopolymer per surface area of aggregate should be in the range of 0.300-0.500 mg/mm2.

Brittleness Generation Mechanism and Failure Model of High Strength Lightweight Aggregate Concrete

The brittleness generation mechanism of high strength lightweight aggregate con-crete(HSLWAC) was presented, and it was indicated that lightweight aggregate was the vulnerable spot, initiating brittleness. Based on the analysis of the brittleness failure by the load-deflection curve, the brittleness presented by HSLWAC was more prominent compared with ordinary lightweight aggregate concrete of the same strength grade. The model of brittleness failure was also established.

Effect of Pre-wetted Light-weight Aggregate on Internal RelativeHumidity and Autogenous Shrinkage of Concrete

This research indicates that the gradient of internal relative humidity （IRH） decreases rapidly within 7-day curing age in HPC. The amount of water imported by pre-wetted light-weight aggregate can regulate IRH of concrete. By importing a proper amount of water, the process of the decline of IRH can be delayed and the autogenous shrinkage can be reduced. The relationship among the amount of water imported by pre- wetted lightweight aggregate, IRH and AS was established. The result provides a new method of reducing early AS and enhancing early cracking resistance of HPC.

Preparation of Novel Core-shell Non-sintered Lightweight Aggregate and Its Application in Wallboard for Better Properties

Due to the relatively high density of conventional non-sintered lightweight aggregate(NLA),a low-density core-shell NLA(CNLA) was developed.Moreover,two types of porous lightweight aggregate concrete (PLAC) for wallboard were designed,using both foam and lightweight aggregates.The effects of LA on lightweight concrete workability,compressive strength,dry shrinkage,and thermal conductivity were studied and compared.The bulk density of CNLA can be lowered to 500 kg/m^(3),and its cylinder crushing strength is 1.6 MPa.PLACs also have compressive strengths ranging from 7.8 to 11.8 MPa,as well as thermal conductivity coefficients ranging from 0.193 to 0.219 W/(m·K^(-1)).The CNLA bonds better to the paste matrix at the interface transition zone,and CNLA concrete has a superior pore structure than SLA concrete,resulting in a 20% improvement in fluidity,a 10% increase in strength,a 6% reduction in heat conductivity,and an 11% decrease in drying shrinkage.

Properties Evaluation of Concrete using Local Used Bricks as Coarse Aggregate

With time concrete / reinforced concrete has become the popular material for construction. Modern industry utilizes this material a lot and has produced various beautiful, eye catching and amazing structures. Due to modern requirements for living and developed construction industries, the old buildings (usually constructed with brick masonry) are demolished and are replaced with new modern buildings. Demolition of buildings results in waste materials which can create waste related problems and environmental issues. By using recycled aggregates weight of concrete can also be reduced, which can also solve problems related to self-weight of concrete. In this paper attempt has been made to use local used bricks from vicinity of Nawabshah, Pakistan, as coarse aggregate. Concrete cubes made with local recycled bricks are cast and tested for overall weight of concrete, moisture content, dynamic modulus of elasticity and compressive strength (nondestructive and destructive methods). The results showed that concrete derived from recycled aggregates attained lower strength than regular concrete. More detailed elaborated work is recommended with different mix ratios and different proportions recycled aggregates for better conclusions.

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.

A Research on the Usage of Corn Cob in Producing Lightweight Concrete

In this study, the possibility of using corn cobs as an organic aggregate in producing lightweight concrete has been investigated. First, some important physical properties of corn cob have been determined in the laboratory. These properties are as follows: weight to volume ratio (unit weight), water absorption rate and granulometric analysis. Later on, 4 concrete mixtures have been prepared according to the workability of concrete and standards specified in Turkey. After that, unit weight, heat transmissibility coefficient and 28-day pressure strength of these 4 concrete samples have been determined using machines measuring these properties. The 28-day pressure endurance value has been found between 1.4 - 56.25 kgf/cm2, heat transmissibility coefficient has been found between 0.19 - 0.35 Kcal/m∙h∙˚C and unit weight of samples have been found between 800 - 1520 kg/m3. Lastly, these properties of concrete samples have been compared with other lightweight materials being used in the construction of buildings.

预置轻骨料混凝土与普通轻骨料混凝土的性能对比

研究了相近强度等级(LC40)下预置轻骨料混凝土与普通轻骨料混凝土的物理性能与耐久性能。结果表明:相同强度等级下,预置轻骨料混凝土密度较普通轻骨料混凝土降低约200 kg/m^(3);同时具有更好的匀质性(上下质量差仅为0.14%,普通轻骨料混凝土为1.68%)与体积稳定性(干缩为普通轻骨料混凝土的1/3)。但由于轻骨料自身强度与弹性模量低,相同强度等级预置轻骨料混凝土的脆性增大,抗折强度与弹性模量降低;并且大量轻骨料堆积提供水分与离子传输通道,抗氯离子扩散性能以及抗冻性能也会降低。

废弃黏土砖骨料轻质混凝土正交试验研究

将废弃黏土砖骨料应用于轻质混凝土中,可实现建筑垃圾再利用,同步节省建筑材料,改善轻质混凝土性能。以废弃黏土砖颗粒为骨料,开展轻质混凝土制备试验,研究不同水灰比、泡沫掺量、纤维掺量对废弃黏土砖骨料轻质混凝土的物理力学性能影响。结果表明:水灰比对吸水率影响显著,随着水灰比的增大,吸水率增加了27.03%,泡沫掺量对干密度、抗压强度和劈裂抗拉强度影响显著,随泡沫掺量的增加,干密度、抗压强度和劈裂抗拉强度减小了17.78%、52.52%和34.83%,并建立了抗压强度与干密度、劈裂抗拉强度之间的对应关系式。

废黏土砖骨料轻质混凝土物理力学性能试验研究

将废弃黏土砖破碎成骨料用于制备轻质混凝土,可同步达到资源再利用、降低环境污染、节省天然骨料的目的。为揭示废弃黏土砖骨料轻质混凝土的性能,通过室内试验对废砖骨料级配、废砖骨料体积率、水灰比、泡沫掺量等因素影响轻质混凝土的干密度、吸水率、抗压强度性能进行试验研究,结果表明:泡沫掺量对干密度和抗压强度影响显著,泡沫掺量由2%增加到5%时,干密度由1407kg/m^(3)减小到1128kg/m^(3),抗压强度由13.39MPa减小到4.66MPa,废砖骨料级配对吸水率影响显著,骨料级配从A组到C组级配时,吸水率由11.3%减小到5.7%。

轻骨料混凝土的研究进展与应用前景

介绍了轻骨料混凝土的特性,分析了轻骨料配合比设计方法,综述了国内外近年来不同轻骨料混凝土受各因素影响的性能研究进展,探究了轻骨料混凝土的微观表象,指出了轻骨料混凝土存在的如工作性较差、可泵送性易受阻等缺陷不足,给出了合理建议,对轻骨料混凝土的未来发展方向和应用前景做出了展望。

火山渣粒径和DPS掺量对轻骨料混凝土性能的影响

以火山渣作为粗骨料制备了轻骨料混凝土,研究了火山渣粒径(4.75~9.50、4.75~19.00、4.75~26.00 mm)对轻骨料混凝土坍落度、吸水率和抗压强度的影响,优选出了最佳火山渣粒径。在此基础上,研究了渗透结晶型无机防水剂(DPS)的掺量(0、0.6%、0.8%、1.0%)对轻骨料混凝土性能的影响,并分析了其作用机理。结果表明:随着火山渣粒径的增大,轻骨料混凝土的坍落度降低,吸水率增大,抗压强度先增大后减小,最佳火山渣粒径为4.75~19.00 mm;随着DPS掺量的增加,轻骨料混凝土的坍落度和吸水率降低,抗压强度增大;掺入适量DPS可以有效提高混凝土基体的密实度,从而改善混凝土的性能。