有机质浸染砂水泥土的力学特性及本构关系

为研究海南省海湾地区分布的有机质浸染砂水泥土的力学特性,该文首先对有机质浸染砂水泥土和标准砂水泥土进行无侧限抗压强度对比试验(采用配合比均为熟石灰掺入比7.5%、水泥掺入比20%、水灰比0.45),定量分析养护龄期对其无侧限抗压强度及试样破坏形式的影响。然后对有机质浸染砂水泥土进行单轴抗压试验,获得了水泥土材料的应力-应变全过程曲线、刚度变化规律以及改进邓肯-张本构模型。结果表明:1)有机质浸染砂水泥土试样的破坏类型为塑性剪切破坏和脆性剪切破坏;2)有机质浸染砂水泥土抗压强度随着养护龄期的增加基本呈指数形式增长,但在养护龄期14 d后,增长速度逐渐降低并趋于稳定;3)随着养护龄期增长,水泥土刚度增加。在加载初期,水泥土切线模量随着轴向应变增加而增大,呈现刚度硬化现象;4)基于单轴抗压试验得到应力-应变全过程曲线,可分为2个阶段:塑性阶段、软化阶段;5)通过对应力-应变全曲线的描述,得到了修正的邓肯-张模型,确定模型参数后,与实测数据对比发现,该修正模型可以模拟有机质浸染砂水泥土的应力-应变关系。

Mechanical properties and constitutive relation of cement-stabilized organic matter-disseminated sand

Abstract: Some sandy sediment in the coasts in Hainan province is rich in organic matters and the sand particles might be coated and disseminated by organic carbon. This could alter the surface of the sand and thus compromises the mechanical strength of the concrete made using such sands as aggregates. This paper experimentally investigated how organic-disseminated sand particles impact the mechanical properties and constitutive equation of the associated concrete. The sample species were prepared by mixing 20% (w/w) and 7.5% of lime with water at water: cement ratio of 0.45; they were then further mixed with sand particles disseminated by organic carbon coating. Concrete using standard sands served as the control. The mechanical properties and constitutive equation of the specimens were measured using the unconfined and uniaxial compressive tests. The unconfined compression test was to measure the compressive strength at curing time of 7d, 14d, 21dand 28d, respectively, and their failure mode. The uniaxial compression test was to measure the stress-strain curve, the stiffness variation rule and the modified Duncan-Zhang constitutive equation. The results show that 1) the failure mode of the concrete with organic-disseminated sands was plastic shear failure and brittle shear failure, while the failure mode of the specimens with standard sand at the same curing time was brittle shear failure. 2) The compressive strength of the concrete with organic- disseminated sands was significantly smaller than that with standard sands at early stage of the curing, although both increased exponentially with the curing time. The compressive strength of each specimen reached asymptotically to a constant after 14 days of curing. 3) The stiffness of the concrete with organic- disseminated sands increased with curing time. After the loading was applied, its shear modulus increased with the axial strain initially, but when the strain reached about 2%, the shear modulus started to decrease with a further increase in strain. In terms of plasticity, the former is known as stiffness hardened and the latter is known as stiffness softening. The stiffness of the concrete with organic-disseminated sands increased with curing time, and the peaked shear modulus at Day 28 is 4.36 times that at Day 7. 4) The stress-strain curve of the concrete with organic-disseminated sands was a interplay of various deformation processes under uniaxial load, and can be divided into two stages: plastic stage and softening stage. 5) The modified Duncan-Zhang model was obtained to describe the full stress-strain curve. Comparison with measured data showed that the model adequately described the stress-strain of the concrete with organic-disseminated sand particles.