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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.

Power Ultrasound (PUS) is widely used in various technical processes (from pharmaceutic to ceramic and fuel industry) to disperse suspensions and to control crystallization processes. Previous investigations by the authors have shown that a short PUS treatment during mixing process effectively accelerates the growth of strength determining C-S-H phases and thus hydration and setting of Portland cement pastes.

The present study concerns the workability, the strength development and the durability of sonicated concretes. Results of study shows, that flowability is increased after sonication and stiffening of cement paste can be fully compensated. The strength development is significantly accelerated and durability testing on sonicated concretes reveals that negative effects of PUS on carbonation behaviour, freezing/thawing- and sulphate-resistance can be excluded. The advantage of using PUS to accelerate early-strength development of concrete is that little or no chemical accelerators or heat treatment are required. Enhancement of cement reactivity by PUS application during mixing possibly paves the way for application of cements with low CO₂-footprint for precast concrete production.

In this paper, the influence of the specific bacterial nutrient (yeast extract) and the precipitation precursors (urea and Ca-nitrate) on cement hydration and mechanical properties were first investigated. Meanwhile, the availability of the nutrient after being mixed into the cementitious matrix was examined. Due to the harsh conditions of concrete (high alkalinity and small pore size), bacteria need to be immobilized beforehand. Therefore the properties of the carrier candidates used for immobilization were also evaluated on the aspects of the pore properties and the compatibility with the cementitious matrix. Experimental results show that yeast extract greatly retarded cement hydration and had a remarkable negative effect on the strength of the mortar. The strength was greatly decreased when the addition was higher than 0.34%. The precipitation precursors had moderate effect on the strength and the optimal dosage was 4% for urea and 8% for Ca-nitrate by the mass of cement. Argex had a much higher porosity (50%) than that of Lava (16%), and had a more suitable pore size distribution for immobilization of bacteria. Both of them had a good compatibility with the cementitious matrix.

Since replacement of portland cement by other cementations materials is one of the main strategies to reduce the environmental impact of cementitious mixture, several innovative portland-free binders have been investigated. This paper is aimed to study a ground granulated blast furnace slag (precursor) activated with a mixture in powder form (activator) of sodium metasilicate pentahydrate, potassium hydroxide and sodium carbonate to manufacture portland-free mortars for conservation, restoration and retrofitting of existing masonry buildings and concrete structures. Several activator/precursor combinations (2%-32% by mass) were used to investigate the effect of alkali activation on the rheological, elastic and physical performances of repair mortars. The experimental data show that by changing the activator/precursor combination it is possible to “tailor” the 28-day compressive strength of the mortar. The activator dosage represents the key parameter influencing not only mechanical performance but also the hydraulic shrinkage: the higher the activator dosage, the more pronounced the mortar shrinkage. Shrinkage values for alkali-activated mortars (AAM) are significantly higher (2000 – 4000 ∙ 10-6) compared with those of cement-based mortars with the same compressive strength. Consequently, a reduction of shrinkage by means of shrinkage reducing (SRA) and/or water retention admixtures is necessary. However, although shrinkage is very high, the modulus of elasticity is about 40% lower than that of a portland cement mortar of the same strength level. On the basis of the experimental data AAMs seem to be more promising for a sustainable future in construction since the GER (Gross Energy Requirement) and GWP (Global Warming Potential) are dramatically reduced by 80 - 90% and 70 - 80%, respectively compared with traditional portland cement mortars with the same compressive strength.

Three proportions of municipal solid waste incineration(MSWI) bottom ash (abbreviated as slag) mixed with sand were used as fine aggregate to make concretes with strength grades of C20, C30, C40, and C50.Workability and strength development were evaluated. Experimental results show that appropriate proportions of slag mixed sand could be used as fine aggregate in medium and low-strength concrete. The proportion of 5:5 slag mixed sand can be used to prepare concrete from grades C20 to C50; the proportion of 6:4 slag mixed sand can be used to prepare concrete from grades C20 to C40; and grades C20 and C30 concrete can be prepared by using the proportion of the 7:3 slag mixed sand. In the range of C20 to C50, the cost of the raw materials for concrete that is made using slag mixed sand is lower equal to the cost for concrete made with river sand. Thus, the former has economic and environmental advantages. It is concluded that the 5:5 slag mixed sand is the optimum proportion.