Soft soil is widely distributed in Vietnam, especially in the coastal area. In engineering practice, soft soil cannot be used to build any construction and needs to be improved or treated before building construction. In addition, Vietnam has many pig-iron or thermal power plants, which annually produce a huge amount of granulated blast furnace slag (GBFS). Thus, the use of this material for soft soil improvement needs to be considered. This paper presents experimental results on the unconfined compressive strength (UCS) of three Vietnam’s soft soils treated with Portland cement and Portland cement with ground granulated blast furnace slag (GGBFS). Binder dosage used in this study is 250, 300, and 350 kg/m3 with the three different water/cement ratios of 0.8, 0.9, and 1.0, respectively. The research results showed that the UCS of soil-cement mixtures depends on soil type, water/cement ratio, cement type, and binder content. Accordingly, the unconfined compressive strength increased with the increase of binder contents, the decrease of the natural water content of soft soil, water/cement ratios, and clay content. The highest value of UCS of treated soils was found for the soil at Site II with the Portland cement content, cement GGBFS, and water/cement ratio of 873 kg/m3, 2355 kg/m3, and 0.8, respectively. Besides, for all the three soils and two binder types, the water/cement ratio of 0.8 was found to be suitable to reach the highest UCS values of treated soil. The research results also showed that the UCS of treated soil with cement GGBFS was higher than that of treated soil with Portland cement. This indicated the effectiveness of the use of Portland cement with GGBFS in soft soil improvement. There is great potential for reducing the environmental problems regarding the waste materials from pig-iron plants in Vietnam and the construction cost as well.
In Vietnam, a large amount of coal bottom ash (CBA) is being discharged from thermal power plants and has been making serious environmental pollution. It is essential to utilize the CBA to reduce environmental pollution. So, this paper presents a series of experimental studies in the laboratory using CBA as a partial replacement of aggregates in concrete pavement for rural roads. In mixing concrete, the CBA is utilized to replace 15, 30, and 100% aggregates. The design of the composition must achieve the technical requirement of M-30 grade of concrete. A total 351 of specimens were tested on workability of fresh concrete, abrasion, compressive strength, and flexural tensile strength in order to achieve the technical requirement of concrete pavement for rural roads. Based on the experimental results, in order to achieve the required compressive strength, An Khanh CBA concrete uses more content of cement and water than control concrete; Cao Ngan CBA is only utilized to replace 15% aggregates, and Cao Ngan CBA concrete also uses more cement and water than control concrete. It also shown that the amount of water and cement content depend on types of CBA and the water amount and cement content of CBA concrete are larger than those of control concrete. The advantage of mixture CBA concrete is abrasion, and flexural tensile strength achieved the value as per the technical requirement.
This paper presents experimental and simulation results of the change in the chloride diffusion coefficient of concrete C40 (f’c=40 MPa) during axial loading. Test Method for Electrical Indication was used to measure the chloride diffusivity of the concrete sample during the axial loading. A mesoscopic lattice model is proposed to describe the variation of chloride diffusion coefficient versus damage variable. In such a model, the domain of material is discretized randomly by using Voronoi tessellation for the transport element and Delaunay triangulation for a mechanical element. At the mesoscale, the concrete is constituted by three phases: aggregate, cement paste and ITZ, in which aggregate is assumed to be elastic while cement matrix and ITZ are represented by a damage model with softening. The experimental and numerical results show that in the first stage, without crack (s < 40%smax), the chloride diffusion coefficient remains almost constant, however in the crack initiation and propagation stage (s = 60-80%smax) chloride diffusion coefficient increases significantly. An empirical power model is also proposed to describe the increase of the chloride diffusion coefficient versus stress level and damage variable.
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