锦北灌渠混凝土污水环境下干湿、冻融交替作用力学试验研究

为研究锦北灌渠工程混凝土在干湿、冻融污水环境下力学特征影响变化,设计开展了污水溶液、物理作用两种因素下的力学试验,并基于试验数据开展了应力应变特征分析。试验表明,不论是干湿或是冻融作用,污水浓度愈高,混凝土承载应力愈弱,但冻融作用下峰值应力受污水浓度影响敏感性更高。改变污水浓度,在干湿作用下应力应变趋势特征具有一致性,但在冻融作用下差异性显著。干湿或冻融交替次数增加,试样峰值应力均下降,在围压30MPa下,交替次数增加2次,干湿、冻融作用下峰值应力分别平均降低了12.3%、20.8%。混凝土受冻融作用影响敏感性高于干湿作用。

非标准混凝土试样力学性能试验研究

我国现行标准规定混凝土抗压强度测试的标准试样为边长150 mm的立方体,在实际工程中存在由于难以获取标准试样,而只能以非标准混凝土试样进行强度检测的情况。通过对某工程在素混凝土桩上取得的非标准混凝土试样进行室内力学试验,结合内维尔公式和岩石尺寸修正系数公式,研究了非标准混凝土试样与150 mm标准立方体试样的强度转化关系,探究了在实际工程中不同公式换算混凝土强度的准确性。试验结果表明,对于高径比2∶1的非标准试样,由岩石尺寸修正系数公式换算的标准立方体抗压强度与实际测得的标准强度较为吻合;对于高径比1∶1的非标准试样,由岩石尺寸修正系数公式换算的标准立方体抗压强度与由内维尔公式换算的标准立方体抗压强度相差不大。

Test and Numerical Analysis on Performance of Reinforced Concrete Segment in Subway Tunnel

To investigate the mechanical behavior of segmental lining, a three-dimensional numerical analysis and test using three actual segments were used to analyze the effects of axial force and reinforcement ratio on the failure mechanism and ultimate bearing capacity of segmental lining. Both numerical and test results confirmed that the cracking load, yield and ultimate load were strongly influenced by axial force, and it was also proved that the yield and ultimate load would increase with the increase of reinforcement ratio, but the cracking load was almost not affected. The cracking load, yield and ultimate load are about 28.7%, 500% and 460% larger due to the effect of axial force respectively. The comparison between numerical calculation and test results showed that the finite element analysis resuits were in good agreement with the test results.

Influence of Recycled Construction Materials Aggregate on Mechanical and Physical Properties of Concrete

The main purpose of this research is to study the properties of re-use different types of construction materials such as PVC （polyvinylchloride） scraps, clay brick and recycled concrete as a partial replacement of coarse aggregate. Different proportions （1%, 3%, 5% and 7%） by weight were used for PVC. scrap, （10%, 20%, 30%, and 40%） by weight were used for recycled concrete and （5%, 10%, 15%, and 20%） by weight were used for clay brick. Mechanical tests such as compressive and tensile strength tests and physical tests such as ultrasonic pulse velocity, bulk density, porosity, specific gravity and water absorption tests were done to the samples after curing in normal water for 28 days. Test results showed slightly degradation in mechanical and physical engineering properties of concrete specimens that used partial replacement of recycled concrete coarse aggregate, degradation increased with increasing of replacement but test results still closely to reference samples. Use of polyvinyl chloride in proportions not more than 5% as a partial replacement of coarse aggregates given acceptable results in comparison with reference samples but all test results degraded at 7% replacements. Test results of partial replacement of crushed brick coarse aggregates unacceptable and the range of degradation are wide because of increased （water： cement） ratio to improve the concrete workability.

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.

Experimental study on mechanical behavior of high performance concrete under multi-axial compressive stress

Experimental investigation was conducted to characterize the responses of high performance concrete(HPC) subjected to multiaxial compressive stresses. The HPC specimens were prepared with three different mix proportions, which corresponds to three different uniaxial compressive strengths. The cubic specimens with size of 100 mm for each edge were tested with servo-hydraulic actuators at different stress ratios. The principal stresses and strains of the specimens were recorded, and the failure of the cubic specimens under various stress states was examined. The experimental results indicated that the stress states and stress ratios had significant influence on the strength and deformation of HPC under biaxial and triaxial compression, especially under triaxial compression. Failure criteria were proposed for the HPC specimens under biaxial and triaxial compressive loading. The test results provided a valuable reference for obtaining multi-axial constitutive law for HPC.