The influence of limited concentration, of 0.025 wt.% per cement weight, poly (ethylene oxide) -block -polystyrene vesicles on the hydration process, microstructure and micromechanical properties of cement paste at early hydration age of maximum 7 days are discussed. Isothermal calorimetry and non-evaporable water content tests indicate that the admixed vesicles have no apparent influence on the process of cement hydration, but affect microstructural properties. Whereas nitrogen adsorption tests reveal that the gel pore structure of the vesicles-modified matrix is almost identical to the vesicles-free one, mercury intrusion porosimetry proves refined capillary porosity and reduced total porosity in the presence of admixed vesicles. Nano-indentation supports the above observations and indicates that the admixed vesicles act as nucleation sites, leading to a more uniform distribution of low density hydration products.
In the Hokuriku district, the effort toward the production of highly durable concrete mixtures using classified fine fly ash has just started as a part of ongoing countermeasures for the chloride attack and the alkali silica reaction (ASR). At a time when ASR deterioration phenomena are still progressing, the use of fly ash cement in concrete should be recommended and assertively be adopted as a regional approach for the mitigation of ASR problem especially in the Hokuriku District. In order to promote this mutual understanding and cooperation among the electric power companies, the national and local governments, the industrial association of ready-mixed concrete companies and the universities are indispensable. Accordingly, a joint-collaborative industry-academia-government research committee has been set up in January 2011. This paper focuses on the drawing from the current stage of ASR problem in the Hokuriku district and the development of highly durable fly ash concretes as its countermeasures.
The durability of concrete structures depends on the mass transfer resistance of cover concrete, which is a primary factor controlling the deterioration caused by carbon dioxide and other penetrants. Therefore, the quality of cover concrete is very important for ensuring the durability of concrete structures. This research examined the influences of mix proportions and construction work conditions on the variation in quality of cover concrete using the on-site air permeability test. However, the influence of concrete water content on the measurement results and the measurable depth of the test are not yet clearly understood, so this effect also needs to be clarified first. Our experimental results showed that the relationship between water content and air permeability is mostly the same regardless of the W/C and concrete thickness, and the measurable depth is between 15 to 40 mm depending on the air permeability. In addition, the air permeability can be formulated as a function of the W/C and the amount of bleeding water, and the change in air permeability over the height of a concrete structure can be expressed by the amount of bleeding water and the height.
This research paper describes the development of strain hardening cement based composite (SHCC) with mostly local ingredients available in Stellenbosch, South Africa, and subsequent characterisation of crack distributions under various loading conditions. The mechanical induced cracking behaviour of SHCC containing local coarse sand (CS) (particle size up to 2.36 mm) is reported and compared with SHCC containing specially graded local fine sand (FS) (particle size up to 300 μm). Crack width distributions, obtained by digital image correlation, in direct tension at various average strain levels are presented for both FS and CS-SHCC dumbbell specimens. Both these SHCC types were also used to prepare beam specimens, both unreinforced and reinforced with steel bar at two reinforcement levels and with three cover depths. Both sand types could be used successfully for SHCC, achieving strain hardening and crack width and spacing control.
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