Microstructural analysis of recycled concrete using X-ray microtomography (original) (raw)
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Multiple recycled aggregate properties analysed by X-ray microtomography
Construction and Building Materials, 2018
The increasing production of construction and demolition waste (C&DW) and the ever-greater consumption of natural resources is forcing society to search for alternatives in order to reduce both. Fortunately, many studies have analysed the possibility of producing recycled aggregates (RA) using old concrete from C&DW [1-6], precast industries [7-10] and industry wastes [11-13]. However, the use of RA against the use of natural aggregate (NA) for structural concrete on material performance, environmental benefits and financial viability of the studies conducted so far do not fully demonstrate the choice of production of recycled aggregate concrete (RAC) with a significant advantage [14]. RA influences the physical and mechanical properties of RAC. The direct influence of the quality of RA on the durability is analysed in [7,15] showing that RA coming from precast-structural concretes is one of the most adequate in order to produce RAC. In terms of durability, the incorporation of recycled aggregate was responsible for worse results but did not compromise their use in structural concrete [16,17]. The properties of the interfacial transition zone (ITZ) have a significant impact on the macro mechanical properties of concrete [18]. X-ray computed axial tomography (CT) provides cross-sectional views of materials, components, and assemblies for non-destructive evaluation [19]. It can be used to examine concrete [20] and the high-resolution X-ray micro-CT allows modelling the permeability of cementitious materials [21]. On the one hand, the irregular surface of the old adhered mortar of the RA contributes to the improvement of the physical bond between the old and new cement matrix [22]. On the other hand, the lower mechanical resistance due to the adhered mortar contributes to reduce the compressive strength [15] and significantly so in the case of dynamic rather than static loading [3,23-25] but no significant influence of the recycled aggregate content on the durability performance of concrete exposed to aggressive environments is detected after years [26]. Multiple recycled aggregate properties analysed by X-ray microtomography C. Thomas a, ⁎
Micro- and macro-porosity of dry- and saturated-state recycled aggregate concrete
Journal of Cleaner Production, 2018
Society is becoming aware of the environment and progressively using more recycled aggregates to produce recycled structural aggregate concrete. In addition, many researches have analysed the properties of hardened recycled aggregate concrete, but few of them have focused on the mixing method and the consequences that it has on the properties of concrete. In this research, recycled aggregate concrete using dry, with extra water supply, and saturated recycled aggregate has been prepared. The different mixing conditions induce differences the micro and macroporosity of concrete that have been evaluated by computerized axial tomography, scanning electron microscopy and a new developed methodology, based on digital image analysis, developed to analyse the distribution and size of macroporosity. The software has been implemented in Matlabã and is available to the readers of the journal for downloading and use. The results show that the dry and saturated recycled aggregate lead to very different concrete properties. On the one hand, the use of dry aggregate causes a local reduction of the w/c ratio, increasing heterogeneity and decreasing workability. On the other hand, the saturated aggregate incorporates extra water by adsorption that causes an increase in the water/cement ratio, thus increasing the porosity volume and size of the new mortar of the recycled aggregate concrete.
Microstructural Characterization of Concrete Prepared with Recycled Aggregates
Microscopy and Microanalysis, 2013
Several authors have reported the workability, mechanical properties, and durability of concrete produced with construction waste replacing the natural aggregate. However, a systematic microstructural characterization of recycled aggregate concrete has not been reported. This work studies the use of fine recycled aggregate to replace fine natural aggregate in the production of concrete and reports the resulting microstructures. The used raw materials were natural aggregate, recycled aggregate obtained from a standard concrete, and Portland cement. The substitution extent was 0, 10, 50, and 100 vol%; hydration was stopped at 9, 24, and 96 h and 28 days. Microscopy was focused on the cement/aggregate interfacial transition zone, enlightening the effect of incorporating recycled aggregate on the formation and morphology of the different concrete hydration products. The results show that concretes with recycled aggregates exhibit typical microstructural features of the transition zone in normal strength concrete. Although overall porosity increases with increasing replacement, the interfacial bond is apparently stronger when recycled aggregates are used. An addition of 10 vol% results in a decrease in porosity at the interface with a corresponding increase of the material hardness. This provides an opportunity for development of increased strength Portland cement concretes using controlled amounts of concrete waste.
Micro-structural analysis of recycled concretes made with recycled coarse concrete aggregates
journal paper, 2021
h i g h l i g h t s At 180-day, the SEM showed a large number of pores at the mortar surface and ITZ of RAC. Removal of the CH crystals around the RCA was mostly observed in the fully RC containing 10% of SF. Compared to CC, using 10% of SF, the compressive strength of RAC can raise to 17%. At high percentages of FA and Z replacement, multiple cluster pores and increment in ITZ thickness of RAC was detected.
2015
Aim of this work was to investigate the microstructure of the Interfacial Transition Zone (ITZ) between cement paste and aggregate in concrete utilizing Scanning Electron Microscope (SEM) in order to identify possible effects on the ITZ related to different recipes and production parameters. SEM is an important tool to carry out concrete, cement and aggregate microstructure characterization. SEM imaging facilitates identification of elements in concrete. Thanks to the higher spatial resolution, and the analytical capabilities, it allows to perform a materials-imaging-related analysis. Many information can thus be extracted from these data, such as composition, phase abundance and distribution. In particular, during the last years, backscattered electron imaging of polished surfaces became an important method for the study of cement and concrete microstructures. The technique has many advantages, as the possibility to visualize representative cross-sections over a wide range of magni...
Analysis of Pore Distribution and Connectivity in Concrete Using X-Ray Microtomography
2015
In the paper a method of X-ray microtomography (micro-CT) was employed for a direct insight into a microstructure of concrete with a practical resolution of approx. 10 micrometers. Two sets of specimens were subjects of examination. The spatial concentration of air pores was investigated in three concretes differing in the amount of the supplement of high calcium fly ash (HCFA). The parameter of pore connectivity called diffusive tortuosity was determined in three other concretes made of the same ingredients but differing in water to cement ratio. The quantitative results obtained with application of described procedures are applicable in material
X-Ray Microtomography System Applied in Characterization of Lightweight Concrete Structures
Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems
Microtomography is a powerful non-destructive method that allows the visualization of the internal structure of the object and makes possible to generate internal graphic models of the object. Concrete is a mixture widely used in the construction industry due to the union between its mechanical properties with the low cost for its production. The application of X-ray microtomography in lightweight concrete structures allows the visualization of the layout and formation of existing internal structures. In this work, it was possible to identify the presence of ethyl vinyl acetate (EVA) and piaçava fibers in the internal structure of the samples and to classify the high-density aggregates according to the ASTM C125-18 standard, as well as to evaluate the influence of the light aggregates in the increasing of the total porosity.
Civil Engineering and Architecture, 2023
Deficiency of natural resources in construction industry is one of the major issues in today's construction era. Another major problem, which not only construction industry, but the entire world is facing, is the management of construction and demolition (C&D) waste. Therefore, it becomes inevitable to recycle the C&D waste and to replace it partially with natural aggregate so as to reduce the strain on natural resources. Recycled concrete aggregates (RCAs) cannot be directly reused as it possesses poor quality in terms of physical and mechanical properties. The objective of this experimental work is to improve the properties of RCAs by using pretreatments such as mechanical abrasion, water soaking, acid soaking, and heating. It is found that using mechanical abrasion, weak acid soaking and moderate heating, the micro structure of the RCA is improved. Water absorption and porosity are improved by 20% and 17.75% respectively. Using pre-treated RCAs, with partial and complete replacement for natural aggregates, concrete cubes were cast and tested for evaluation of compressive, split tensile and flexural strengths. Compressive strength for 40% replacement is improved by 17.41% as compared with the M25 grade concrete made using natural aggregates. Also, replacement by 100% is possible and compressive strengths are comparable. Thus, using the pre-treatments, C&D waste utilization, reduction in consumption of natural aggregates (NA) is possible in medium grade applications leading to sustainable construction.
Micro-Mechanical Performance of Concrete Used as Recycled Raw Material in Cementitious Composite
Acta Polytechnica CTU Proceedings, 2017
The reduction of industrial pollution is recently one of main goals over all fields. In civil engineering, recycling of structural waste provides wide opportunity contributing this effort. This paper focus on re-use of concrete waste, which after further processing can be used in new constructions as partial supplement to the mixture. To investigate the impact of recycled concrete addition, it is necessary to determine mechanical and structural parameters of individual phases in the "raw" material. For this purpose, grid indentation and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM, EDX) are combined to determine properties of concrete sample.