Wenzhong Zhu

Permeation properties of self-compacting concrete

Permeation properties, which include permeability, absorption, diffusivity etc., have been widely used to quantify durability characteristics of concrete. This paper presents an experimental study on permeation properties of a range of different self-compacting concrete (SCC) mixes in comparison with those of selected traditional vibrated reference (REF) concretes of the same strength grade. The SCC mixes with characteristic cube strength of 40 and 60 MPa were designed containing either additional powder as filler or containing no filler but using a viscosity agent. The results indicated that the SCC mixes had significantly lower oxygen permeability and sorptivity than the vibrated normal reference concretes of the same strength grades. The chloride diffusivity, however, appeared to be much dependent on the type of filler used; the SCC mixes containing no additional powder but using a viscosity agent were found to have considerably higher diffusivity than the reference mixes and the other SCCs.

Application of nanotechnology in construction Summary of a state-of-the-art report

The paper is an extended summary of the state-of-the-art report on Application of Nanotechnology in Construction, which is one of the main tasks of a European project Towards the setting up of a Network of Excellence in Nanotechnology in Construction (NANOCONEX). The paper first presents background information and current developments of nanotechnology in general. Then, the current activities and awareness of nanotechnology in the construction industry are examined by analysing results of a survey of construction professionals and leading researchers in the field. This is followed by results of a desk study of nanotechnology development and activities focussing on key areas relevant to construction and the built environment. Examples of nanotechnology-enabled materials and products that are either on the market or ready to be adopted in the construction industry are provided. Finally, the future trend/potential and implications of nanotechnology development in construction are discussed. 2. I N T R O D U C T I O N

Uniformity of in situ properties of self-compacting concrete in full-scale structural elements

Abstract Inadequate homogeneity of the cast concrete due to poor compaction or segregation may dramatically lower the performance of mature concrete in situ. To ensure adequate compaction and facilitate placement of concrete in structures with congested reinforcement and in restricted areas, self-compacting concrete (SCC) has been developed. Considering the highly flowable and self-levelling nature of the SCC, there are general concerns that segregation and settlement may occur during its transport and placing. This study was designed to provide information on uniformity of in situ properties of SCC mixes in practical structural columns and beams and to compare results with those of properly compacted conventional concrete. The in situ concrete properties were assessed by testing cores for in situ strength, pull-out of pre-embedded inserts and rebound hammer number for near-surface properties. The results indicated that there were not significant differences in uniformity of in situ properties between the SCC mixes and the corresponding well compacted conventional mixes.

Assessment of interfacial microstructure and bond properties in aged GRC using a novel microindentation method

Changes of microstructure and properties in the interfacial zone of glass fibre reinforced cement (GRC) under the effect of ageing were investigated. A novel technique based on a microindentation apparatus was developed and successfully used to carry out microstrength testing in the interfacial area and push-in tests on selected individual fibres within a strand. By continuously monitoring load vs. displacement, the new technique allowed the microstrength to be measured in small, porous areas of the fibre-matrix interfacial zone, and particularly within the glass fibre strand/bundle. The results showed that the embrittlement of aged GRC was closely associated with a substantial increase of the microstrength values within the fibre bundle during the ageing process. It was also revealed that a wide range of bond properties existed within the fibre strand. The resistance to fibre sliding was much greater at the outer filaments than at the inner central filaments of the fibre strand/ bundle.

Structure, composition and mechanical relations to function in sea urchin spine

Sea urchins have characteristic spines that fulfil critical functions. Several studies revealed marked spine internal heterogeneities at different structural levels despite the single-crystal character of the spines. Most of these studies did not speculate about the functional meaning of these heterogeneities. Spine heterogeneities were investigated in the sea urchin Paracentrotuslividus and their possible functional implications discussed. Spines mainly show two morphological parts: the base, made of a meshwork stereom, and the shaft, with longitudinal plain septa and a central core of meshwork stereom. Electron Backscatter Diffraction showed no difference in crystallite orientation between the two structures. Atomic Absorption Spectrometry and Energy dispersive X-ray analysis revealed that Mg was not uniformly distributed in the spine. Mg concentration is higher in the inner part of the septa than in the septum outer part. Furthermore, a cyclic pattern of Mg concentration in septa was observed. This is suggested to be linked to the spine ontogeny. Nano- and microindentation analyses revealed that the septa have higher stiffness and hardness than the meshwork stereom and that septum stiffness and hardness present different trends in longitudinal and transverse section. These mechanical heterogeneities may have an adaptive functional value.

Nanotechnology in Construction

Nanotechnology and Construction in the 21 Century From nanotechnology to new production systems: the EU perspective Nanotechnology in civil engineering Nanotechnology: business and investment opportunities Integration of European nanotechnology research in construction Application of nanotechnology in construction - current status and future potential Nanotechnology for construction beyond the imagery Techniques and Instrumentation Focused Ion Beams (fib) - tools for serial sectioning of nanoindentation sites in cementitious materials Micro - an intermediate step to nano level analysis in concrete like composites Applications of DualBeam in the analysis of construction materials Synchrotron-Radiation X-ray Tomography: a method for the 3d verification of cement microstructure and its evolution during hydration Observation of the nanostructure of cement hydration by Soft X-ray Transmission Microscopy Study of pozzolan-cement interaction by Atomic Force Microscopy (afm) Estimation of the degree of hydration and phase constitutions by the SEM-BSE image analysis in relation to the development of strength in cement pastes and mortars Modification of cement paste with silica fume - a NMR study Modelling Modelling and temperature dependence of microstructure formation in cement based materials Numerical modelling of volume changes in cement-based systems at early ages Numerical modelling and experimental observations of the pore structure of cement-based materials Virtual concrete: working at the nanometer scale Evaluation of theoretical models for assessing interfacial properties in aged grc using fibre push-in test Moving-window representation of interfacial debonding in concrete Molecular modelling of confined fluids and solid-fluid interfaces in Portland cement and related materials Density functional calculation of elastic properties of portlandite and foshagite Exploring the micro-mechanics of open-ended pile driving via discrete element modelling Materials and Products Nanostructure of single carbon fibres investigated with synchrotron radiation High-performance nanostructured materials for construction Synthesis and characterization of nanoparticulate calcium aluminates Effects of water-cement ratio and curing age on the threshold pore width of hardened cement paste Effect of curing regime and type of activator on properties of alkali-activated fly ash Take a closer look: calcium sulphate based building materials in interaction with chemical additives Investigation of the micro-mechanical properties of underwater concrete Applications Thin films and coatings: atomic engineering The Nanohouse(TM) - an Australian initiative to develop the home of the future Building fapade integrated quantum dot concentrated solar electricity production Microsystems for the control of cable vibration Carbon nanotubes and their application in the construction industry Nano-science and -technology for asphalt pavements Natural roofing slate: the use of instrumented indentation technique to measure changes in the elastic modulus and hardness due to weathering Use of instrumented indentations for quality control of building materials Subject Index.

Application of depth-sensing microindentation testing to study of interfacial transition zone in reinforced concrete

Abstract A new method, the depth-sensing microindentation technique, was successfully used to study the elastic modulus and micro-strength of the interfacial transition zone (ITZ) around steel reinforcement in practical reinforced concrete. A normal concrete mix and a special self-compacting concrete (SCC) mix, both produced commercially, were used in the study. It was found that the elastic modulus and microstrength in the ITZ were significantly lower on the bottom side of a horizontal steel reinforcement than on the top side. The difference was particularly pronounced in the 10–30 μm distance from the actual interface. The method showed clear advantages over the conventional Vickers microhardness test.

Material properties of brachiopod shell ultrastructure by nanoindentation

Mineral-producing organisms exert exquisite control on all aspects of biomineral production. Among shell-bearing organisms, a wide range of mineral fabrics are developed reflecting diverse modes of life that require different material properties. Our knowledge of how biomineral structures relate to material properties is still limited because it requires the determination of these properties on a detailed scale. Nanoindentation, mostly applied in engineering and materials science, is used here to assess, at the microstructural level, material properties of two calcite brachiopods living in the same environment but with different modes of life and shell ultrastructure. Values of hardness (H) and the Young modulus of elasticity (E) are determined by nanoindentation. In brachiopod shells, calcite semi-nacre provides a harder and stiffer structure (H∼3–6 GPa; E=60–110/120 GPa) than calcite fibres (H=0–3 GPa; E=20–60/80 GPa). Thus, brachiopods with calcite semi-nacre can cement to a substrate and remain immobile during their adult life cycle. This correlation between mode of life and material properties, as a consequence of ultrastructure, begins to explain why organisms produce a wide range of structures using the same chemical components, such as calcium carbonate.

Ocean acidification alters the material properties of Mytilus edulis shells

Ocean acidification (OA) and the resultant changing carbonate saturation states is threatening the formation of calcium carbonate shells and exoskeletons of marine organisms. The production of biominerals in such organisms relies on the availability of carbonate and the ability of the organism to biomineralize in changing environments. To understand how biomineralizers will respond to OA the common blue mussel, Mytilus edulis, was cultured at projected levels of pCO2 (380, 550, 750, 1000 µatm) and increased temperatures (ambient, ambient plus 2°C). Nanoindentation (a single mussel shell) and microhardness testing were used to assess the material properties of the shells. Youngs modulus (E), hardness (H) and toughness (KIC) were measured in mussel shells grown in multiple stressor conditions. OA caused mussels to produce shell calcite that is stiffer (higher modulus of elasticity) and harder than shells grown in control conditions. The outer shell (calcite) is more brittle in OA conditions while the inner shell (aragonite) is softer and less stiff in shells grown under OA conditions. Combining increasing ocean pCO2 and temperatures as projected for future global ocean appears to reduce the impact of increasing pCO2 on the material properties of the mussel shell. OA may cause changes in shell material properties that could prove problematic under predation scenarios for the mussels; however, this may be partially mitigated by increasing temperature.

Effect of microsilica and acrylic polymer treatment on the ageing of GRC

Abstract Microsilica and acrylic polymer dispersions were used in different types of fibre treatments and matrix modifications. The effects of the various treatments/modifications on the flexural properties, the failure modes and the interfacial changes after different periods of ageing were investigated. The fibre treatment was found to be more effective in controlling the interfacial changes and properties of the aged composites, compared to the matrix modification. The relative effectiveness of the different fibre treatments, however, depended greatly on the bundle size of the fibre reinforcement used. A new technique based on an unique microindentation apparatus was developed and used to carry out micro-strength testing in the fibre-matrix interfacial zone and particularly within the fibre bundle. Results suggested that a soft/flexible fibre bundle core combined with a strong bonding at the fibre-matrix interface was desirable for the optimal improvement of the long term performance of the composites.