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 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.

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.

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.

Experimental study of lightweight aggregate concrete under multiaxial stresses

Lightweight aggregate concrete cube specimens (100 mm×100 mm×100 mm) and plate specimens (100 mm×100 mm×50 mm) were tested under biaxial compression-compression (CC) and compression-tension (CT) load combinations. For comparison, normal concrete plate specimens (100 mm×100 mm×50 mm) were tested under the same load combinations. Based on the test results, a two-level strength criterion of lightweight aggregate concrete in both octahedral stress coordinate and principal stress coordinate was suggested. The lightweight aggregate concrete cube specimens (100 mm×100 mm×100 mm) were then tested under triaxial compression-compression-compression (CCC) load combination with corresponding tests on normal concrete cube specimens (100 mm×100 mm×100 mm). The effect of intermediate principal stress on triaxial compressive strength is further examined. A "plastic flow plateau" area was apparent in principal compressive stress-strain relationships of lightweight aggregate concrete but not in normal concrete. A quadratic formula was suggested for the expression of strength criterion under triaxial compression.

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.