A microstructural insight into the hygro-mechanical behaviour of a stabilised hypercompacted earth

The use of raw earth as construction material can save embodied and operational energy because of low processing costs and passive regulation of indoor ambient conditions. Raw earth must however be mechanically and/or chemically stabilised to enhance stiffness, strength and water durability. In this work, stiffness and strength are enhanced by compacting raw earth to very high pressures up to 100 MPa while water durability is improved by using alkaline solutions and silicon based admixtures. The effect of these stabilisation methods on hygro-mechanical behaviour is explored and interpreted in terms of the microstructural features of the material. Stiffness and strength are defined at different humidity levels by unconfined compression tests while the moisture buffering capacity is measured by humidification/desiccation cycles as prescribed by the norm ISO 24353 (Hygrothermal performance of building materials and products determination of moisture adsorption/desorption properties in response to humidity variation. International Organization for Standardization, Geneva, 2008). As for the microstructural characterisation, different tests (i.e. X-ray diffractometry, Infrared Spectroscopy, Mercury Intrusion Porosimetry, Nitrogen Adsorption) are performed to analyse the effect of stabilisation on material fabric and mineralogy. Results indicate that the use of alkaline activators and silicon based admixtures significantly improves water durability while preserving good mechanical and moisture buffering properties. Similarly, the compaction to very high pressures results in high levels of stiffness and strength, which are comparable to those of standard masonry bricks. This macroscopic behaviour is then linked to the microscopic observations to clarify the mechanisms through which stabilisation affects the properties of raw earth at different scales.     

Durability of lightweight OPS concrete under different curing conditions

The use of waste materials and by products from different industries for building construction has been gaining increased attention due to the rapid depletion of natural resources. It has been found that oil palm shell (OPS), which is a waste from the agricultural sector, can be used as coarse aggregate for the manufacture of structural lightweight concrete. However, for OPS concrete to be used in practical applications, its durability needs to be investigated. Therefore, this paper presents the durability performance of OPS concrete under four curing regimes. The durability properties investigated include the volume of permeable voids (VPVs), sorptivity, water permeability, chloride diffusion coefficient and time to corrosion initiation from the 90-day salt ponding test, and Rapid Chloride Penetrability Test (RCPT). Results showed that the durability properties of OPS concrete were comparable to that of other conventional lightweight concretes and proper curing is essential for OPS concrete to achieve better durability especially at the later ages.     

A new prefabricated external thermal insulation composite board with ceramic finishing for buildings retrofitting

Given the high energy consumption connected to old buildings and their large environmental impact, there is a strong need for effective solutions for the building envelope retrofitting. Among these solutions, external thermal insulation composite systems (ETICS) have found large application in recent decades. In this paper a new kind of large-size thermal insulation composite boards, prefabricated using porcelain stoneware slab finishing, was developed. Different thermal insulating materials and adhesives, with and without glass fibre mesh, were tested by both current methodologies and purposely designed tests, in order to assess their physical–mechanical properties and durability performance, finally selecting the most suitable materials for the composite board. The strong points of this composite board are mainly: (i) its short placing time and improved execution quality, due to prefabrication; (ii) its high aesthetical value; (iii) its high durability, as the finishing layer is mostly insensible to weathering. The results highlight the good performances of the prefabricated composite board developed in this study (generally higher than current ETICS). The testing procedure followed in this study is also meant to give a contribution to the establishment of methodologies for the selection and durability assessment of materials for the building envelope retrofitting.     

一类新型碱激发胶凝材料催化剂的研究进展

碱激发固体铝硅酸盐胶凝材料是先进无机非金属材料的前瞻性研究领域之一, 本文对碱激发铝硅酸盐胶凝材料的分类、制备工艺、形成机理以及潜在的应用前景进行了综述; 详尽地论述了碱激发胶凝材料基新型催化剂的最新研究进展, 综合分析了碱激发胶凝材料作为结构材料研究的局限性, 展望了该材料作为新型催化材料的发展动态。     

Accelerated climate ageing of building materials, components and structures in the laboratory

Building materials, components and structures have to fulfil many functional demands during the lifetime of a building. Therefore, it is important to require satisfactory durability of these materials, components and structures. In fact, one single material failure may jeopardize whole components as well as structures. Unfortunately, experience shows that building products too often do not satisfy the various requirements after a relatively short period of use, i.e. the expected service life is considerably shorter than foreseen. This results in increased and large costs due to increased maintenance, extensive replacements of the specific building products and any possible consequential building damages. In addition, health hazards with respect to both risk and consequence may also become an issue. To avoid this, the solution is to apply building products which have properly documented adequate and satisfactory long-term durability. That is, building products which have been subjected to long-term natural outdoor climate exposure or appropriate accelerated climate ageing in the laboratory. This study examines the main climate exposures and how these may be reproduced in the laboratory in various ways. Thus, crucial properties of building products and their durability towards climate strains may be investigated within a relatively short time frame compared with natural outdoor climate ageing. Examples of miscellaneous climate ageing laboratory apparatuses, ageing methods and building product properties to be tested before, during and after ageing are given. A calculation method for estimating acceleration factors is also discussed. Various ageing examples are shown and discussed. A special note is made towards accelerated climate ageing of new and advanced materials being developed. Hence, this study addresses durability and the versatile and powerful application of accelerated climate ageing which is an all too overlooked field within materials science and engineering.     

Microbial impact on building materials: an overview

Microbial activity can have an important impact on the durability of building materials. It is important to understand this activity in order to select appropriate treatment strategies for the repair and restoration of buildings and monuments. This paper describes the microorganisms which can modify the properties of building materials such as concrete, mortars, composites, timber, gypsum, etc., as well as the mechanisms responsible for deterioration of these materials. The information provided by the members of TC 183-MIB via a questionnaire is discussed. Techniques currently utilised and areas requiring further study are identified. In addition to the references, a list of publications for further reading completes this article.

     

Developments on vegetable fibre–cement based materials in São Paulo,Brazil: an overview

Vegetable fibres, which are widely available in most developing countries, can be used as convenient materials for brittle matrix reinforcement, even though they present relatively poor durability performance. Taking into account the fibres mechanical properties, with an adequate mix design, it is possible to develop a material with suitable properties for building purposes. In order to improve the durability of vegetable fibres, this paper presents the approach adopted in the research which is directed towards the development of alternative binders, with controlled free lime, using ground granulated blast furnace slag. Coir fibres demonstrate to be more suitable vegetable fibres for the reinforcement of large components as can be proved by in-use durability performance evaluation of an 11-year old prototype house. More recently, pulp from eucalyptus waste and residual sisal and coir fibres have been studied as a replacement for asbestos in roofing components.     

An overview of mechanical properties and durability of glass-fibre reinforced recycled mixed plastic waste composites

In recent years, there has been an increasing interest in seeking the potential applications of recycled mixed plastic wastes in building and construction sectors to relieve the pressure on landfills. This paper presents the recent developments and applications of composite materials made from recycled mixed plastics and glass fibre. Some of the first uses for such composites are as an alternative to non-load bearing applications like park benches and picnic tables. With its inherent resistance to rot and insect attack, these composites can in fact be used as a replacement for chemically treated woods in various larger-scale outdoor applications such as railroad crossties and bridges. However, the properties of the structural components made from recycled mixed plastics are not well understood. Information on the behaviour of such composites under applied loading and at different environmental conditions such as elevated temperature and ultraviolet rays are crucial for the utilisation of recycled mixed plastic materials in construction. This paper presents an overview of the mechanical properties and durability of recycled mixed plastic waste composites. The paper identifies research needs critical in the effective design and utilisation of these composite materials in civil engineering and construction.     

Effect of rice-husk ash on durability of cementitious materials

In this paper the effects of partial replacements of Portland cement by rice-husk ash (RHA) on the durability of conventional and high performance cementitious materials are investigated. Different percentages of RHA replacement levels, two RHAs (amorphous and partially crystalline optimized by dry-milling) and several water–cementitious materials ratio are studied. The following durability aspects were tested: air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance. The results were compared with those of cementitious materials without RHA. It is concluded from the tested properties that the incorporation of both RHAs in concretes show different behaviors for air permeability and chloride ion penetration depending on the water/cementitious materials ratio used; in mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction. The results of durability aspects due to physical or pozzolanic effects after the addition of both RHAs, and its chemical composition, in general indicate an enhanced performance, proving the feasibility of its rational utilization as a supplementary cementing material.     

A review on durability properties of strain hardening fibre reinforced cementitious composites (SHFRCC)

This paper reviews and presents various durability properties of strain hardening fibre reinforced cementitious composites (SHFRCC). Published research results show that, due to its tight crack width properties compared to ordinary concrete and ordinary fibre reinforced concrete, SHFRCC significantly resists the migration of aggressive substances in to the concrete and improves the durability of reinforced concrete (RC). It is also reported that, due to the strain hardening and multiple cracking behaviours, SHFRCC meets the tight crack width limits for durability of RC structures proposed by different design codes. Based on the reviewed durability properties it is argued that SHFRCC materials can be used in selected locations of RC structural members to improve their overall durability performances.     

地质聚合物混凝土研究现状

地质聚合物混凝土是一种新型绿色建筑材料,以来源广泛的工业固体废弃物为原材料,能耗小、碳排放低、制备方便,并且抗压抗折强度、抗酸碱侵蚀性能、冻融性能、抗碳化性能优异,具有广阔的应用前景,是普通硅酸盐水泥基材料的最佳替代物之一.本文回顾了地质聚合物混凝土的国内外研究进展,综述了原材料组成、配合比设计、工作性、力学性能以及耐久性等几个方面的发展状况,评述了地质聚合物混凝土技术所面临的问题.     

地质聚合物混凝土研究现状

地质聚合物混凝土是一种新型绿色建筑材料,以来源广泛的工业固体废弃物为原材料,能耗小、碳排放低、制备方便,并且抗压抗折强度、抗酸碱侵蚀性能、冻融性能、抗碳化性能优异,具有广阔的应用前景,是普通硅酸盐水泥基材料的最佳替代物之一。本文回顾了地质聚合物混凝土的国内外研究进展,综述了原材料组成、配合比设计、工作性、力学性能以及耐久性等几个方面的发展状况,评述了地质聚合物混凝土技术所面临的问题。     

Durability of building materials: Durability research in the United States and the influence of RILEM on durability research

This paper is based on the text of a talk given at a RILEM Seminar on Durability of Building Materials. It reviews some of the recent non-proprietary research on the durability of building materials carried out in the US. It also reviews activities in RILEM which have stimulated the generation or dissemination of knowledge on durability of building materials. The paper emphasizes the need for international collaboration in durability research. Member of RILEM Technical Advisory Group International Union of Testing and Research Laboratories for Matérials and Structures. Based on a talk by James R. Wright, RILEM Seminar on Durability of Building Materials, Tokyo, Japan, October 13, 1984.     

超高强水泥基材料的力学及耐久性能

超高强水泥基材料作为一种高性能建筑材料,在建筑工程领域已得到了广泛的关注和应用。简要介绍了超高强水泥基材料的发展历史、制备的基本途径和性能实现的基本原理,并且对近年来国内外学者关于超高强水泥基材料力学性能和耐久性能的研究进展进行了综述。综述内容包括:超高强水泥基材料的抗压强度、抗折强度、弹性模量、泊松比、应力应变曲线,以及超高强水泥基材料的抗渗、抗冻性能和碱骨料反应风险。在对已有文献的综述基础上,简要分析了纤维及养护制度对超高强水泥基材料性能的影响,并提出了超高强水泥基材料工程化的关键措施。     

Controlled fabrication of branched Fe nanotubes

Here, we report a generic synthetic approach to rationally design hierarchically branched nanopores inside anodic alumina membranes (AAMs). By using these nanopores, a large variety of branched nanotubes, which are far more complex than that exists nowadays, can be fabricated. As an example, Y-branched Fe nanotube arrays have been successfully synthesized by electrochemical deposition method using these kinds of AAMs. The length and diameter of the nanotubes, determined by the thickness and the outside pore diameter of the AAMs, are about 7–8 μm and 200 nm, respectively. This technique provides a powerful approach to produce nanostructures of greater morphological complexity, especially branched nanotubes of various kinds of materials, which might be of significant applications in the electronic nanodevices and nanocircuit.     

Effect of etch-treatment upon the intensity and peak position of photoluminescence spectra for anodic alumina films with ordered nanopore array

Porous anodic alumina membranes (AAMs) were prepared in oxalic acid and then carried on an etch-treatment in phosphoric acid. Using the etch-treatment the photoluminescence (PL) intensity of AAMs increases by a factor of 1/3. The effect of etch-treatment upon the intensity and peak position of photoluminescence (PL) spectra was investigated. It was found that the intensity of the photoluminescence (PL) spectra increased with the etching time increasing. A PL spectrum can be divided into two subbands with the peak at 434 and 460 nm, respectively. As the etching time prolongs, the intensity of the peak of 434 nm subband increases and that of the 460 nm subband rises firstly and then decreases. It can be explained by that two luminescence centers (F and F⁺ centers) coexist in AAMs. F centers are concentrated in the surface layer and F⁺ centers are enriched in the depth of pore wall. The increment of the PL intensity comes from the contribution of F⁺ photoluminescence centers concentrated in the depth of pore wall in AAMs. This work will be beneficial to improving the photoluminescence intensity and understanding the light-emitting mechanisms for related materials.     

核防护用水泥基中子屏蔽材料的研究进展

不同能量的中子有不同的工程屏蔽方法,水泥基中子屏蔽材料具有重要应用价值.本文首先从中子防护的角度简要介绍了中子屏蔽原理,其次从快中子减速、慢中子吸收两个方面总结概括了水泥基中子屏蔽材料的研究现状,分析了水泥基中子屏蔽材料存在的不足:功能单一、耐久性、施工性及环境友好等问题,并指出了下一步研究方向:提高核防护水泥混凝土综...     

Effect of heat capacity and physical behavior on strength and durability of shale, as building material

Increasing use of rock materials like shale in building, roofing, embankment filling, brick manufacturing, and in other civil structure application makes it an important rock to consider in construction engineering. Knowledge of thermal and physical properties of shale as building material is required to predict the rock??s strength and permanence against weathering. Inconsistent heat capacity of anisotropic rock can result in differential heat flow. This tendency can expand the building materials leading to reduction in strength and initiate disintegration. Authors have studied various thermo-physical properties of anisotropic shale from Tennessee, which is commonly used as building stones and bricks. Experiment was designed to measure the basic thermal property, ??heat capacity?? of shale. Series of laboratory tests including durability, strength, specific gravity, moisture content, and porosity were conducted to determine the physical and mechanical behavior of the samples. Results indicated that properties like porosity, strength and heat capacity varied significantly within samples, where as specific gravity and moisture content yielded steady values. Multivariate regression analysis was performed to evaluate possible correlations among the tested properties. Strong positive relationship was evident between heat capacity, and porosity. Heat capacity and Unconfined Compressive Strength of shale were inversely related. This study emphasized that physical and thermal properties of shale are directly linked with strength and durability of the rock mass.     

Identification of Logarithmic-Type Creep of Calcium-Silicate-Hydrates by Means of Nanoindentation

Abstract:  In order to relate the complex macroscopic behaviour of concrete with finer-scale properties of cement paste, aggregates, porous space, etc. multiscale models are developed. Here, in addition to homogenisation schemes establishing the relation between the properties of the constituents, e.g. matrix and inclusions, and the properties of the composite material, experimental methods for identification of finer-scale properties are required. Recently, the elastic properties of the main clinker phases in ordinary Portland cement (OPC) and calcium-silicate-hydrates (CSH) were identified by nanoindentation (NI). In this paper, the NI technique is extended towards identification of the viscous, time-dependent behaviour of CSH, i.e. the main finer-scale binding phase in OPC-based material systems. Hereby, a logarithmic-type creep behaviour is identified, corresponding perfectly to the creep behaviour encountered for mortars and concrete.