No abstract

Self-healing structures mimic the ability of biological structures (e.g. bone) to redistribute their structural mass in response to dynamic service loads and damaging effects. The self-healing features yield enhanced levels of structural efficiency and safety in dynamic service environments. In this study, the piezoelectric effect was used to convert the dynamic mechanical energy applied to the structure into electrical energy that, in turn, was used to drive electrochemical selfhealing phenomena within a solid electrolyte. A theoretical framework was developed for self-healing materials, and experiments were conducted to verify the fundamental principles of the approach. The theoretical models confirmed that: (1) the piezoelectric effect can, within the geometric and mechanical constraints of actual structural systems, generate sufficient electric potential and charge (through harvesting the available mechanical energy) to enable electrochemical mass transport within a solid electrolyte; and (2) the redistribution of structural mass in dynamic service environments can occur within viable time frames. The fundamental principles of the new self-healing materials were validated through the demonstration of piezo-induced electrolytic phenomena in solid electrolytes and by verifying the gains in mechanical performance associated with such phenomena. KeywordsSelf-healing, piezoelectric effect, mechanical performance, solid electrolyte, electrolysis Bond, 2005) has increased the interest in this technique. Kersey et al. (2007) have reported two general categories of the self-healing techniques available for recovery of mechanical properties. Self-healing is noted to occur either through the creation of new chemical bonds within the material, for example, by in situ polymerization of monomers in cracks or by re-creation of the ruptured chemical bonds as demonstrated by Chen

The concept of using milled waste glass as partial replacement for cement in cement paste and mortar was investigated to reduce the adverse environmental and energy impacts of cement and cement-based products. Based on the experimental investigations it was found that waste glass, when milled to micro-scale particle size, undergoes pozzolanic reaction with cement hydrates. These reactions bring about favourable changes in the structure, including pore system characteristics of the hydrated cement paste and mortar. Use of milled waste glass, as partial replacement of cement, produced significant gains in the resistance to moisture sorption, chemical stability and improvement in microstructure of the cementitious materials. Milled waste glass was also found to suppress alkali–silica reactions. Unlike normal pozzolanic reactions, those involving glass do not reduce the alkalinity of cement paste; this is favourable to the chemical stability of cement-based materials and the protection of reinforcing steel against corrosion in concrete.alues derived using available design codes.

No abstract

About 12.5 million tons of waste glass is generated annually in the U.S., 77% of which is disposed of in landfills. Waste glass can be cost-effectively collected in mixed colors, but has limited markets. Mixed-color waste glass offers desired chemical composition and reactivity for use as a supplementary cementitious material for enhancing the chemical stability, moisture resistance and durability of concrete. To realize this potential, waste glass needs to be milled to micro-scale particle size for accelerating its beneficial chemical reactions in concrete. In this investigation, recycled glass concrete was produced by partial replacement of cement with milled waste glass. Recycled glass concretes with 15, 20 and 23 wt.% of cement replaced with milled glass were investigated in field (pavement) construction projects. The compatibility of recycled glass concrete with conventional construction techniques was evaluated, and the field performance of recycled glass concrete under weathering effects (in mid-Michigan) was monitored over a two-year period. Compressive strength, water sorption, chloride permeability, and abrasion resistance tests of recycled glass concretes were performed on cores drilled from the experimental pavements, and the results were compared with those obtained with normal concrete. Flexural strength tests were carried out on concrete specimens at various ages. Test results indicated that recycled glass concrete incorporating milled waste glass as partial replacement for cement offers excellent strength and durability attributes when compared with normal concrete. The pozzolanic reactions of milled waste glass with cement hydrates improve the microstructure and chemical composition of concrete. Use of milled waste glass in concrete as partial replacement of cement represents an important step towards development of sustainable (environmentally friendly, energy-efficient and economical) concrete-based infrastructure systems.

No abstract

Use of milled waste glass, as partial replacement for cement, to overcome the drawbacks of recycled aggregate concrete was investigated. Based on experimental investigations of the structure and properties of concrete materials, it was found that waste glass, when milled to micro-scale particle size, undergoes pozzolanic reactions with cement hydrates, forming secondary calcium silicate hydrate (C–S–H). These reactions bring about favourable changes in the structure of the hydrated cement paste and the interfacial transition zones in normal and recycled aggregate concrete. Use of milled waste glass, as partial replacement of cement, produced significant gains in mechanical properties, dimensional stability, and abrasive effects, of recycled aggregate and normal concrete. Milled waste glass was also found to suppress alkali–silica reactions. Recycling of waste glass in concrete can divert large quantities of the market-limited (mixed-colour) waste glass from landfills for value-added use as partial replacement for cement, enable effective use of recycled aggregates in concrete, yield major cost and energy savings, and enhance the long-term performance and the sustainability of concrete-based infrastructure systems.

In this work the characteristics of recycled aggregate concrete produced with crushed stone sand as 100% replacement of desert stone were experimentally investigated. Concrete mixtures incorporating varying percent replacement of normal aggregate with recycled aggregate as coarse aggregate and crushed stone sand as fine aggregate were produced and tested at 7, 28, 56 and 90 days of concrete age for various hardened concrete properties. For one-on-one comparison, corresponding recycled aggregate concrete mixtures using desert sand as fine aggregate were also tested. Superior performance of crushed stone sand-based concrete mixtures was recorded for compressive and flexural strengths, static modulus of elasticity, abrasion resistance and water absorption characteristics when compared with that of the corresponding recycled aggregate concrete mixtures produced with desert sand as fine aggregate. No significant effect of crushed stone sand was recorded on the split tension strength of concrete mixtures. Improvement in mechanical properties and water absorption characteristics of crushed stone-based mixtures was, however, observed up to 50 wt.% replacement level of normal aggregate with recycled aggregate. Beyond this level of replacement, no noticeable difference in the performance of the two categories of recycled aggregate concrete mixtures was recorded. It is concluded that crushed stone sand can be effectively used as fine aggregate replacing desert sand to avoid the limitations caused in the mechanical properties of recycled aggregate concrete mixtures due to the use of desert sand as fine aggregate.