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In October 30 to November 2, 2018, the CCS and the China Academy of Building Research (CABR), Beijing China, in association with the COIC sponsored the Fourteenth International Conference on Recent Advances in Concrete Technology and Sustainable Issues in Beijing, China. The proceedings of the Conference consisting of 19 refereed papers were published by the ACI as SP 330. In addition to the refereed papers, more than 52 papers were presented at the conference, and these were published in the supplementary papers volume.

The applicability of Natural Rubber Latex (NRL) as film forming agent was tested in mortar.

Two NRL samples, a commercial concentrated and a laboratory-treated, deproteinized one, were compared with a commercial synthetic ethylene-vinylacetate (EVA) copolymer regarding their particle size distribution, surface charge and minimum film forming temperature (MFFT). Additionally, a potential retarding effect of the dispersions was investigated by heat flow calorimetric measurements. Cement mortars holding 2 percent by mass of the dispersions were tested for their strength development after 1, 3, 7 and 28 days.

NRL exhibits an average particle size of 350 nm, possesses a highly anionic charge and possesses a MFFT of ~1 °C (34 °F). Heat flow measurements show that the non-treated NRL retards cement hydration. Mortar tests revealed that both NRL samples showed slightly higher strength values than the industrial EVA latex. However, the NRL latexes require addition of a PCE superplasticizer to achieve workability and strong defoamers.

Based on detection technology of helium pycnometry, the study developed a novel approach for studying absolute volume change of Portland cement in early-age hydration process. Traditional methods, such as heat evolution, chemical shrinkage test (ASTM C 1608) and X-ray diffraction (XRD), were also adopted for comparison and analyzation. Results indicated that helium pycnometry is quite suitable in the study of the absolute volume change of Portland cement. Compared with chemical shrinkage test, the data captured by helium pycnometry is more accurate and efficient for analyzing the absolute volume change of Portland cement. Meanwhile, helium pycnometry is found to have a good correspondence with the traditional methods, the trends of which are almost the same. According to the trends of the absolute volume change and heat flow, hydration process of Portland cement can be divided into five stages, which are dissolution stage, induction stage, acceleration stage, deceleration stage and stable stage.

The relationships of diffusivities and age factors between the analytical and empirical models for chloride diffusion in concrete having a decreasing diffusivity are established. Apparent diffusivities and age factors in the empirical model are determined by fitting the chloride profiles obtained from the analytical model. The instantaneous diffusivities in analytical model are smaller than the corresponding apparent values. The ratios of two diffusivities decrease with time and age factor. Logarithm ratio of apparent diffusivity to the reference value at early age is proportional to the logarithm time ratio only after 2.5 years but not before while that of instantaneous diffusivity is so for all the time. The empirical model is suitable only when all inputs are determined based on the data after 2.5 years but not before. Furthermore, the ratio between hypothetical apparent diffusivity at reference time and the corresponding instantaneous value is obtained.

In order to improve compressive strength and the durability of concrete, such as, alkali-aggregate reaction resistance, chloride ion permeation resistance, carbonation resistance, and freezing and thawing resistance, a new type of combined cementitious materials was used to make the concrete. One part of the cementitious materials was high early strength Portland cement (similar to ASTM type III Portland cement), which had more than 63 mass% C3S and hydrated quickly to generate calcium hydroxide to accelerate pozzolanic reaction. Another part of the cementitious materials was fine blast furnace slag powders which had more than 6000 cm²/g Blaine specific surface area to get faster hydration with the calcium hydroxide. And other part of the cementitious materials was fly ash which had high specific surface area and low ignition loss to get faster pozzolanic reaction. According to the results of tests in this research, it is clear that the compressive strength of the concrete made with the combined cementitious materials is near that of the concrete made with the high early strength Portland cement only. However, the alkali-aggregate reaction in the concrete made with the combined cementitious materials is much lower than that of the concrete made with the high early Portland cement, and/or mixed with the fine blast furnace slag powders or fly ash respectively. It is also confirmed that chloride ion permeation resistance, carbonation resistance, and freezing and thawing resistance of the concrete made with the combined cementitious materials are improved considerably.