Improving environmental sustainability of concrete products: Investigation on MWC thermal and mechanical properties

This research focuses on the possibility of constituting a more sustainable lightweight concrete, Mineralized Wood Concrete (MWC), substituting natural aggregates with wastes from woodworking activities. Exploiting this type of aggregates, a triple purpose has been achieved: preservation of natural raw materials, reuse of wastes and energy saving. Furthermore, the use of wood aggregates is a way to try to develop a sustainable concrete characterized by high thermal inertia, high thermal resistance and low weight.In this paper, effects of the addition of wood aggregates on mechanical and thermal properties of concrete are studied. Mechanical performances have been investigated with compressive strength tests, while a one-dimensional heat flow model has been used to predict the thermal conductivity of MWC.The use of MWC can be associated with the idea of a different typology of relatively heavy building envelope: this union could competitively answer to the demand of well-insulated building envelope and concurrently characterized by high thermal mass. From this union, a series of other values can be derived: low weight, environmentally friendly, easily industrialized and easy on-site casting. Consequently, applications of wood concrete in building constructions may be an interesting solution in order to improve sustainability and building energy efficiency.     

Performance of olive waste ash concrete exposed to elevated temperatures

This study explores the influence of olive waste ash (OWA) on the performance of concrete exposed to elevated temperatures in the range from 400 to 600 °C. The performance of concrete to elevated temperature was evaluated using compressive strength and electrical charge of concrete. Three OWA levels were used in the study: 7%, 15%, and 22% by weight of cement. The other experimental parameters investigated in the study were elevated temperature (400 and 600 °C), aggregate type (crushed basalt and volcanic tuff), w/c ratio (0.5 and 0.7), and air content (non-air and air entrained). After the initial moist curing period of 90 days, concrete specimens were exposed to elevated temperatures for a period of 2 h using an electric furnace.     

Material properties of historical masonry of the Frauenkirche and the masonry guideline for reconstruction

This contribution provides insight into the characteristics of the masonry of the historical Frauenkirche and the requirements for its reconstruction. Comprehensive material studies were performed in the course of preparation for and implementation of the project, and guidelines for evaluation, design and construction were established on the basis of those studies. The material used for the reconstruction is sandstone, coming from quarries in the immediate vicinity, as well as mortar composed on a lime basis with hydraulic additives. The execution is monitored within the scope of a quality management system specially created for the reconstruction project. This system simultaneously provides a detailed documentation of the building materials used in the project.     

低相变点焊条提高纵向焊接接头的疲劳性能

研制一种用于提高焊接接头疲劳强度的新型焊条———低相变点焊条 (LTTE) ,其熔敷金属的马氏体相变温度为 191℃ ,在焊态下 ,LTTE接头纵向焊趾部位获得 -2 5MPa的残余压缩应力。而普通焊条E5 0 15接头相同焊趾部位却为95MPa的残余拉伸应力。利用上述两种焊条分别焊接三种类型的纵向焊接接头 ,并进行疲劳试验。结果证明 ,在 2× 10 6循环次数下 ,LTTE焊接接头的疲劳强度分别比E5 0 15的提高 41%、47%和 5 9% ;在 162MPa的应力幅值下 ,LTTE焊接接头的疲劳寿命分别比E5 0 15的提高 9.9倍、9.6倍和 46.8倍。此外 ,低相变点焊条方法不需增加焊后处理工序 ,是一种有效提高纵向焊接接头疲劳性能的方法     

Creep analysis of concrete containing rice husk ash

This paper presents an experimental study on the mechanical properties of concrete added with rice husk ash (RHA) as a supplementary cementitious material. The compressive strength, modulus of elasticity and creep were obtained experimentally from specimens with different RHA contents (0%, 10%, 15% and 20% of binder). The results show that the addition of RHA in concrete can improve both the compressive strength and modulus of elasticity and reduce the creep of concrete. The examination of pore micro-structure of hardened concrete using both the mercury intrusion porosimetry and scanning electron microscope techniques demonstrates that RHA particles can react with calcium hydroxide originated from cement hydration to produce additional C-S-H, which can fill voids and large pores and thus reduces the porosity related to capillary pores and voids. In addition, the release of absorbed water, which is retained in the small pores of RHA particles at early days, can improve cement hydration and thus reduce the porosity related to gel pores.     

Properties of high volume glass powder concrete

Mechanical and durability properties of concrete with cement replaced by finely grounded glass powder in high volume up to 60% were investigated. XRD and TGA analyses indicated that the fine glass powder reacted with calcium hydroxide to form calcium-silicate-hydrates. As such, the microstructures of concrete were more compact and homogeneous, especially at the interfacial transition zone. Concrete with cement replaced by 15% and 30% glass powder exhibited the highest strength increase and correspondingly the lowest porosity. Beyond a replacement of 30%, calcium hydroxide became insufficient for the pozzolanic reaction of glass powder. However, the high volume glass powder concrete retained distinct resistance against water and chloride ingress, due to the reduction in pore size and connectively. Reductions of 77%, 83%, 96%, 91% and 92% were observed respectively for water penetration depth, sorptivity, conductivity, chloride diffusion and migration coefficients in concrete with cement replaced by glass powder by 60%.     

Compressive strength and microstructure of fly ash based geopolymer blended with silica fume under thermal cycle

This work aims to reveal the effects of silica fume on properties of fly ash based geopolymer under thermal cycles. Geopolymer specimens were prepared by alkali activation of fly ash, which was partially replaced by silica fume at levels ranging from 0% to 30% with an interval of 10%, by mass. Microstructure, residual strength and mass loss of fly ash based geopolymer blended with silica fume before and after exposed to 7, 28 and 56 heat-cooling thermal cycles at different target temperatures of 200 °C, 400 °C and 800 °C were assessed and compared. The experimental results reveal that silica fume addition enhances strength development in geopolymer. Under thermal cycles, the compressive strength of geopolymer decreases, and the compressive strength loss, as well as the mass loss, increases with increasing target temperature. The strength loss is the same regardless of silica fume content after thermal cycles. Microstructure analysis uncovers that pore structure of geopolymer degrades after thermal cycles. The pores of geopolymer are refined by the addition of silica fume. The incorporation of silica fume optimizes the microstructure and improves the thermal resistance of geopolymer. Silica fume increases the strength of the geopolymer and even though the strength loss is the same, the strength after heat cycle exposure is still good.     

Hydration reactions of cement combinations containing vitrified incinerator fly ash

One treatment option for municipal solid waste incinerator fly ash (IFA) is vitrification. The process yields a material containing reduced levels of trace metals relative to the original ash. The material is glassy and potentially suitable as a cement component in concrete. This paper examines the vitrification of an IFA and studies the hydration reactions of combinations of this vitrified material and Portland cement (PC). Isothermal conduction calorimetry, powder X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy were employed to study the hydration reactions. As the levels of vitrified ash increase, the quantities of AFt phase produced decrease, whilst quantities of AFm phase increase, due to the reduced levels of sulfate in the vitrified ash. The levels of calcium silicate hydrate (CSH) gel (inferred from estimates of quantities of gel-bound water) remain constant at 28 days regardless of vitrified ash content, indicating that the material is contributing toward the formation of this product.     

The effects of air content on permeability of lightweight concrete

Air entraining agent is used to control the floatation of lightweight aggregate (LWA) in lightweight aggregate concrete (LWAC), therefore reducing the segregation of LWAC. At the same time, using an air entraining agent will affect the water sorption of the concrete. In this paper, two lightweight concrete mixes of density 1000 kg/m³ and air content of 13.5% and 31.9% were compared and the effects of entrained air on the strength, surface sorptivity, and chloride permeability of LWAC are presented. Results show that the use of porous LWA would not lower the permeability resistance of concrete. Entrained air had little effect on sorptivity but a major effect on chloride permeability. The weaker pores' network in the cement paste is the basic cause for the high chloride permeability of concrete than the use of porous LWA. Although chloride permeability of low density LWAC concrete decreased with age of concrete, it was found that the concrete was not dense enough to stop the chloride ion to penetrate through the concrete before the concrete mature at 90 days.