•The coarser particles needed larger λ to achieve same yield stress of paste.•The relationships between yield stress and λ were established.•λ in binary-cement pastes was evaluated in consideration of particle size.•Reliability of the evaluation of λ was validated experimentally.•This paper gives a deeper insight into initial packing and bridging of particles.The distance between particles (λ) plays a key role in the flowability of fresh cement pastes. λ given in available literatures is an average value and independent with the particle size. Actually, coarse particles in cement paste need a larger λ to achieve same yield stress compared with fine particles. In the present study, relationship between yield stress and λ for single-fraction cement pastes was established by introducing an exponential-type function. Then the function was theoretically deduced to evaluate λ in binary-fraction cement pastes. For cement pastes with yield stress of 30 Pa, distance between coarse particle (48.51 μm) and fine particle (6.63 μm) was 5.00 μm, while distance between mid-sized particle (20.27 μm) and fine particle (6.63 μm) was only 2.57 μm. Finally, the reliability of λ in binary-fraction cement paste was experimentally validated. This method can be applied in multi-fraction cement pastes, and λ in consideration of particle size will give a deeper insight in the flowability and microstructural development of cement pastes.Download high-res image (205KB)Download full-size image

•Changes of Portland cement paste in carbonic acid water were followed.•Carbonic acid water corrosion process of Portland cement paste was described.•A carbonic acid water corrosion model of Portland cement paste was proposed.•A corrosion kinetics was theoretical deduced and fitted with experimental data.Underground concrete structures usually suffer from carbonic acid water corrosion, thus evaluation and prediction of the carbonic acid water corrosion are very important for cement-based materials. Portland cement pastes were immersed into a renewal carbonic acid water, then the corrosion process was followed in this paper. The results show that no obvious corrosion was observed in the first 7 days, while significant corrosion was observed after 28 days corrosion. The corroded zone can be divided into three regions according to the Ca/Si molar ratio of the cross section, where dissolution of CH, carbonation and dissolution of carbonates, and multi-decalcification of hydration products occurred gradually from the internal to the external. Based on the experimental data, a carbonic acid water corrosion model of Portland cement paste was proposed, then the corrosion kinetics, which can be used to predict the carbonic acid water corrosion of Portland cement paste, was theoretically deduced and fitted using the experimental data.

•Ultra-lightweight Portland cement-based foam concretes were successfully prepared.•Collapse and air-void escape can be avoided by adding thickening agent and stabilizing emulsion.•The optimal foaming temperature and W/CM ratio were 45 °C and 0.55, respectively.•Most pores in ultra-lightweight foam concretes were non-connected pores with size of 2.0–4.0 mm.•Ultra-lightweight foam concretes showed lower thermal conductivity, desirable mechanical properties.Due to desirable thermal insulation properties, superior fire-resistant and higher durability, ultra-lightweight foam concretes are recommended to achieve energy efficiency in buildings. Generally, aluminate cement, sulphoaluminate cement and other quick hardening cementitious materials are used to control the stability of air-voids in foam concretes. These special cementitious materials are relatively expensive and not universally available, retarding the application and popularization of foam concretes. In the present study, the proportioning and properties of Portland cement-based ultra-lightweight foam concrete were investigated. The results show that ultra-lightweight foam concretes with apparent density of 100–300 kg/m3 can be prepared using Portland cement, fly ash, hydrogen peroxide and chemical admixtures. Collapse and air-voids escape can be avoided by adding thickening agent and foam stabilizing emulsion into foam concretes. Most of pores in ultra-lightweight foam concretes were non-connected pores with size of 2.0–4.0 mm, resulting in a lower thermal conductivity, desirable compressive and tensile strengths.

•Efficient way to achieve sustainability is utilizing industrial wastes in cementitious materials.•The substitution ratio of industrial wastes in cement is relatively low by traditional methods.•High performance blended cements with higher waste addition can be prepared by novel methods.•Novel methods of incorporating industrial wastes in blended cement are more efficient.•Novel methods lead to significant role in CO2 emissions reducing, resources and energy conservation.Sustainable development and eco-efficiency are urgent and imperative demands for the well-being of our planet, continued growth of a society, and human development. Traditional Portland cement production seems unsustainable due to consumption of huge natural resources and energy and significant CO2 emissions. The volume of industrial wastes is increasing significantly, leading to a number of economical and ecological problems. Although industrial wastes can be incorporated in cementitious materials by various traditional methods, the substitution ratio of industrial wastes in cementitious materials is relatively low to avoid unacceptable performance loss. Novel methods, such as improving hydraulic activities of metallurgical slags by adding composition adjusting material at high temperature, improving surface cementitious properties of fly ashes by dehydration and rehydration treatment, and arranging cement clinker and industrial wastes in the particle size distribution of blended cements according to their hydraulic activities, are reviewed. These methods provide more effective approach to prepare high performance blended cements with larger amount of industrial wastes, leading to a very significant role in CO2 emissions reducing, resources and energy conservation of the cement industry.