土凝岩再生混凝土抗冻耐久性试验研究

为探究土凝岩固化高掺量再生骨料混凝在冻融循环作用下抗冻性能,文中采用快冻冻融试验法、SEM试验,分别对9%、12%、15%剂量土凝岩固化70%、100%的再生骨料混凝土进行冻融循环试验。结果表明土凝岩固化70%掺量再生骨料混凝土抗冻性总体上高于100%掺量,水泥-硅灰处理再生骨料对再生骨料混凝土的抗冻性能有明显提升。随着土凝岩掺量由9%增加至12%和15%,混凝土抗冻性逐渐提升。在相同冻融循环次数条件下,水泥混凝土抗冻耐久性优于土凝岩混凝土,水泥-硅灰处理后的土凝岩混凝土的抗冻性接近P·042.5水泥混凝土。研究可为土凝岩混凝土在寒冷地区工程应用提供理论参考。

Volumetric Variation and Rheology of Cement Based Mineral Additions （Blast Furnace Slag and Silica Fume）

The partial substitution of clinker by mineral additions offers very significant, both economical and environmental benefits. This adds value to industrial waste, and contributes also in the preservation of natural resources, like clay and limestone, as well as the reduction of greenhouse gas emissions （CO2）. This study is interested in the simultaneous effect of BFS （blast furnace slag） and SF （silica fume） on setting time and water requirement of cement paste. The volumetric variations are tested in mortars, prepared in the same mixture of pastes, and the tests indicate that the addition of slag increase the fluidity, reduce the water demand, shrinkage and expansion, compared to the mortar, containing ten percent （10%） of Silica Fume only. The images of pastes obtained by SEM （scanning electron microscopy）, are indicated an improvement of the microstructure of the paste with a large amount of slag, which leads to improve durability.

Effective Use of Cement for Modification of Base Course Material

Cement improves properties of soil materials, such as durability, stiffness, strength and moisture susceptibility. Each of them needs different cement contents that might not be suitable for other properties. Typically, high cement content is desirable for durability, but not for shrinkage and cracking issues on the surface. Thus, improving durability with low cement content while complying with other requirements is an ideal aim, which may be achieved by pozzolanic supplementary products. Pozzolans contribute in hydration reactions and optimise cement consumptions in favour of durable and low shrinkage products. In this paper, the mixes of nano-silica and fly ash are considered to investigate their effect on strength, durability and shrinkage of modified CRB （crushed rock base） material. In the end, the benefits and features of nano-silica as a pozzolanic material will be focused and discussed more for effective cement consumption in soils.

Properties prediction of fly ash blended concrete using hydration model

Fly ash is an industrial by-product from coal combustion and has been widely used as mineral admixture in normal and high strength concretes. Owing to the pozzolanic reaction between calcium hydroxide and fly ash, compared with Portland cement, the hydration of concrete containing fly ash is much more complex. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of concrete containing fly ash. Similar to the hydration reaction of cement, fly ash activity is divided into three processes: an initial dormant period, a phase-boundary reaction process and a diffusion process. The mutual interactions between the cement hydration and fly ash reaction are considered through the available calcium hydroxide amount and available capillary water amount in the system. The properties of hardening fly ash blended concrete, such as the reaction degree of fly ash, chemically bound water, calcium hydroxide, and compressive strength, are determined from the contributions of cement hydration and fly ash pozzolanic reaction. The evaluated results show good accordance with the experimental results.