Materials and Structures最新文献

Taking inspiration from the recent rise in interest on calcined clays, the RILEM technical committee RILEM TC 282-CCL on Calcined Clays as Supplementary Cementitious Materials has been summarising knowledge on a wide variety of topics related to the use of calcined clays in cement and concrete. In this article, the working group 2 of this committee summarises recent global efforts on the industrialisation of calcined clay cements, to bring the work of the committee into context. Clays have been a key construction material since Roman times but are now designated as crucial for enhancing cement industry sustainability in the short to mid-term. Several industrial and semi-industrial trials that have recently produced calcined clays through various techniques, such as static, rotary, and suspension calcination technologies are covered in this paper, while worldwide cement production trials with calcined clays and limestone are also discussed. Major projects considering local clays as construction materials are presented as examples of global interest in the subject. Due to interest in achieving climate goals, calcined clays are being rapidly reintroduced into the cement industry, and academic research has played an important role in this process. The examples discussed in this article demonstrate the importance of greater and swifter knowledge transfer from academia to industry. The work also demonstrates the need to upgrade industrial equipment and design new efficient equipment to eliminate the use of fossil fuels for clay calcination, a process that requires relatively lower temperature than clinker production. The challenges in achieving net-zero carbon emissions in clay calcination technologies are also discussed. Overall, this paper presents the context in which the RILEM TC 282-CCL operated.

Durability studies of basalt fiber reinforced concrete (BFRC) structures are still in their infancy. New breakthroughs are needed in the exploration of the mechanical properties of BFRC under the coupling effect of multiple factors. In order to release the influence of composite chloride-sulfate attack history on the fire resistance of BFRC, mechanical experiments were carried out on BFRC specimens, which were first soaking in a certain concentration of chloride-sulfate composite solution, and then submitted to different high temperatures. The compressive strength, relative dynamic elastic modulus and the residual compressive strength of the specimens after high temperatures were tested. The results show that compared with chloride concentration, sulfate concentration has a greater effect on the compressive strength and relative dynamic elastic modulus of BFRC. The presence of chloride can inhibit the attack of sulfate in the concrete and reduce the change in strength at room temperature. The combined attack of chloride and sulfate aggravates the strength deterioration of the BFRC specimens after high temperatures.

A quantitative characterization of the capillary porosity of cement pastes has been performed in the context of corrosion of aluminium alloy 1100 in contact with Portland cement pastes. The originality of the study is to combine an electrical equivalent circuit model identified based on electrochemical impedance spectroscopy (EIS) data and a two-phase model derived from the general effective media theory (GEM). The effective resistance of the cement paste entering the GEM is approximated by the resistance of connected capillary pores as provided by the EIS analysis to determine the evolving porosity of cement pastes. Mercury intrusion porosimetry data agree with the porosity results obtained from EIS. The porosity in the 0.36 OPC is reduced from ~ 15% to below 10% over the first 30 days and then keeps decreasing slowly, while the porosity of the 0.36 OPC + 3% LiNO₃ samples slightly decreases at the beginning and finally remains constant at ~ 10%. For the 0.50 OPC + 1.607% Li₂CO₃ composition, the porosity decreases from ~ 25% to ~ 15% over the first 30 days. The influence of the curing conditions is also studied to extract the impact on the porosity. Besides, the diffusion of corrosion products is limited to a small region near the interface and hence the corrosion process does not affect the porosity of the cement paste.

Numerous (inter)national standards are in place for assessing the resistance to carbonation of mortar and concrete. Within the framework of RILEM TC 281-CCC ‘Carbonation of Concrete with SCMs,’ an extensive interlaboratory test campaign (ILT) involving twenty-two participating laboratories worldwide was initiated to compare natural carbonation of concrete and mortar with three different cement types (Portland cement (CEM I), Portland-fly ash cement (CEM II/B-V) and blast-furnace cement (CEM III/B)) and investigate its relation to accelerated carbonation as reported in Vanoutrive et al. (Mater Struct 55:1–29, 2022). It could be concluded that ranking of cement types was analogous between accelerated and natural carbonation methods. Environmental parameters have an important effect on the carbonation rate, however, differences between the mean carbonation rates originating from indoor and sheltered outdoor natural exposure with different exposure conditions and curing regimes were insignificant for each considered cement type. This is caused by the scatter related to carbonation testing among different laboratories. Nevertheless, results showed that a natural exposure period of at least one year is essential to reach a constant carbonation rate over time. For both natural and accelerated carbonation, the carbonation rate increased by 18% when the aggregate-to-cement ratio increased by 1.79 (concrete versus mortar). This correlation seems insensitive to binder type and exposure method. Finally, the best correlation between natural and accelerated carbonation was found for EN 12390–10 (specifically natural indoor exposure) and EN 12390–12 (accelerated exposure) when only test methods performed by more than one laboratory were considered.

The RILEM TC 281–CCC ‘‘Carbonation of concrete with supplementary cementitious materials’’ conducted a study on the effects of supplementary cementitious materials (SCMs) on the carbonation rate of blended cement concretes and mortars. In this context, a comprehensive database has been established, consisting of 1044 concrete and mortar mixes with their associated carbonation depth data over time. The dataset comprises mix designs with a large variety of binders with up to 94% SCMs, collected from the literature as well as unpublished testing reports. The data includes chemical composition and physical properties of the raw materials, mix-designs, compressive strengths, curing and carbonation testing conditions. Natural carbonation was recorded for several years in many cases with both indoor and outdoor results. The database has been analysed to investigate the effects of binder composition and mix design, curing and preconditioning, and relative humidity on the carbonation rate. Furthermore, the accuracy of accelerated carbonation testing as well as possible correlations between compressive strength and carbonation resistance were evaluated. One approach to summerise the physical and chemical resistance in one parameter is the ratio of water content to content of carbonatable CaO (w/CaO_reactive ratio). The analysis revealed that the w/CaO_reactive ratio is a decisive factor for carbonation resistance, while curing and exposure conditions also influence carbonation. Under natural exposure conditions, the carbonation data exhibit significant variations. Nevertheless, probabilistic inference suggests that both accelerated and natural carbonation processes follow a square-root-of-time behavior, though accelerated and natural carbonation cannot be converted into each other without corrections. Additionally, a machine learning technique was employed to assess the influence of parameters governing the carbonation progress in concretes.

Reef limestone has special pore structures, which makes its seepage characteristics remarkably different from those of conventional terrestrial tight rocks. In this article, the microscopic structure of reef limestone and the water–cement ratio (WCR), cement fineness, and an admixture on flocculated cement particles were studied. Meanwhile, the probability analysis was adopted to evaluate the injectability for reef limestone cement grouts. The results indicate that the pore size gradually diminishes and the thickness of the wall for cemented walls increases little by little as the density of reef limestone increases. Generally, reef limestone has many seepage channels, indicating strong grout injectivity; when the WCR is larger and the cement fineness is smaller, the number and the size of flocculated cement particles is smaller, so the injectivity of cement grout is improved; this may be enhanced further after use of an admixture. In summary, the volume fraction of flocculated cement particles in cement grouts, as well as the relative sizes of pores and flocculated cement particles, can affect the degree of grout injectability. Injectability results calculated using the theoretical formula based on these influencing factors are found to match those arising from cement-grouting experiments, verifying the practicability and reliability of the injectability probability formula.

Freeze–thaw weathering is commonly attributed to the premature degradation of lime mortars. This study is unique as it explores how the effect of incorporating pozzolanic brick dust, combined with the dewatering mechanism, can influence the resistance to freeze–thaw cycling. The combination of brick dust and hydrated lime constitutes a pozzolanic lime mortar with hydraulic character. Importantly, the addition of brick dust was shown to play a crucial role by modifying the pore structure of the mortar matrix, which affected the water transport kinetics, and durability. This rigorous investigation evaluates the freeze and thaw resistance of hardened young (7-day) and old (180-day) mortars in both dewatered and non-dewatered conditions. Quantitative analysis of the microstructure highlights the role of brick dust and dewatering in densifying the matrix, refining the pore structure, and enhancing the freeze and thaw resistance. The benefits of dewatered brick dust mortars were demonstrated as young-age dewatered mortars showed similar resistance to freeze and thaw compared to the older-age non-dewatered mortars. This was attributed to the reduction of the water/binder ratio due to dewatering. It has been successfully demonstrated that freshly mixed mortars can be enhanced on-site through the addition of brick dust and coupling with a substrate that promotes dewatering. Using this approach to produce mortars with greater freeze thaw resistance will improve longevity and reduce failure rates. Impact will be realised in mortars for both new build and conservation applications.

Masonry is a complex structural material with different properties due to a combination of units and mortar. Masonry has very high compressive strength, but when subjected to lateral forces such as earthquakes, its load-carrying capacity reduces significantly because of low tensile capacity. For this research, an experimental study was carried out to study brick masonry's behaviour and failure pattern. A retrofitting scheme was proposed to enhance in-plane load-carrying capacity under push-over loading conditions. A push-over test was performed on the brick masonry walls, and after failure, it was retrofitted and subjected to loading. The retrofitted wall has increased the masonry's load-carrying capacity and enhanced its ductile behaviour, having a yield drift of 8.63%. As the proposed system undergoes large deformations before failure, the behaviour factor R is calculated as 4.53 for ductility of 10.8. Masonry and its components are characterised by performing laboratory experiments and compared with previous studies. The mechanical properties of brick units, mortar, and masonry prism are obtained according to suitable code procedures. An analytical model based on the virtual work approach is developed to estimate failure patterns and load-carrying capacity. The analytical model predicts a failure pattern for conventional brick walls, the same as the experiment failure pattern.

This paper presents an investigation conducted on a 50-year-old structure in a composite climactic zone of India. The study comprises two parts, one covering the comparison of long-term natural and short-term accelerated carbonation while another revealing insight into the structure’s durability and potential concerns. Mineralogy, pore solution, and transport properties comparison of natural and accelerated carbonated concrete samples highlight similar modifications, demonstrating the representative nature of accelerated carbonation at 3% carbon dioxide concentration. However, accelerated carbonation led to the preferred precipitation of calcite and a higher degree of C–S–H carbonation. Core strength and carbonation depth measurements indicate that the carbonation coefficient shows a high variation within the structure due to micro-climatic conditions, and there is a need to consider carbon dioxide concentration greater than 400 ppm for residential buildings. Additional investigations based on half-cell potential, surface resistivity, and corrosion rate measurement highlighted that moisture availability is the main deterioration-controlling factor during the propagation phase. Also, it was realized that during an inspection, if different non-destructive measurements fall in the middle range, it becomes inconclusive to ascertain the severity of corrosion. In such situations, visual inspection of the reinforcement is imperative. Finally, the authors recommend collecting data on carbon dioxide concentration and the moisture state of different locations in the structure during structural inspection.

For asphalt mixtures, it is widely known that Poisson’s Ratio (PR) varies according to several parameters, and it is a temperature and loading frequency-dependent property. However, measuring PR at different temperatures and frequencies during mechanical tests is not commonly done. For that, a complex arrangement of fixtures and instruments would be necessary, and still likely not compatible with typical cylindrical specimens. This work aimed to combine the simple and practical Ultrasonic Pulse Velocity (UPV) test with the conventional Dynamic Modulus ((|E^*|)) test used for determining pavement design inputs related to asphalt mixtures. To do this, four typical lower binder asphalt concrete mixes were selected, having different levels of Asphalt Binder Replacement (ABR), given the presence of RAP/RAS, and covering seven different asphalt binders in terms of Performance Grade (PG). Additionally, a baseline mixture with no recycled material was used for comparison. Results show that estimating (|E^*|) via UPV assuming a typical PR value may be inaccurate. Once reference experimental modulus values were available, PR was backcalculated using the UPV theory, showing that this property increases as temperature increases, while it decreases as ABR and air voids increases. This indicates that PR can be a source of significant variability when it comes to the use of recycled materials. Therefore, UPV emerges as a low-cost, practical, and reasonably accurate piece of equipment (compared to state-of-practice assumptions) with potential to be integrated with traditional (|E^*|) testing for an assessment of PR sensitivity according to different mixes’ properties.