Production of sustainable and structural fiber reinforced recycled aggregate concrete with improved fracture properties: A review

Fracture behavior of a sustainable material: Recycled concrete with waste crumb rubber subjected to elevated temperatures

Research progress on recycled clay brick waste as an alternative to cement for sustainable construction materials

With increasing population and rising demands for improved built environment, there is an expected increase in greenhouse gas emission from the construction industry. Carbon dioxide emission levels are fast approaching a tipping point which could lead to irreversible climate change. The earth's capability to neutralise the CO2 emissions through the natural carbon cycle has been overstretched. Therefore it is imperative to adopt technologies that are able to capture and sequester CO2 in order to cancel out their release from industrial activities such as the construction and building industry. This is important so that cement-based material productions' carbon footprint can be reduced drastically for a positive change to take place in the climate. Biochar holds great promise as an effective CO2 sorptive material in cement-based applications relatively similar to its conventional use for soil amendment. Actually, fragmented researches on biochar as an admixture in cementitious materials have been conducted. Based on this logic, this review placed enormous emphasis on collating information from recent studies on biochars from agro-sources used as an admixture in cement-based applications. Similarly, the review gave up-to-date knowledge about the sources of the biomass and the production processes. Conclusively, the positive effects of biochar for carbon sequestration on some properties of the various cementitious applications were highlighted.

Recent advancements in the use of biochar for cementitious applications: A review

Characterising the resilient behaviour of pavement subgrade with construction and demolition waste under Freeze–Thaw cycles

To relieve the increasing traffic load, many early built highways need to be widened or reconstructed. The rapid performance detection to existing subgrades is important to their reasonable evaluation and maximized utilization. Based on five kinds of soils taken from an existing highway in southern China, three commonly detecting methods were used to determine their moisture contents, compaction degrees and resilient moduli. The results showed that the measured moisture contents were greater than the design value, and the compaction degrees decreased sharply compared to the original ones. The moisture and heat exchange produced a decrease in the resilient modulus of plate loading test (PLT) from the standard 60 MPa down to 40 MPa. Afterwards, the portable falling weight deflectometer (PFWD) and dynamic cone penetrometer (DCP) were used to evaluate the subgrade performances. The measured PFWD moduli and the DCP penetration rates were correlated with the resilient moduli of PLT, deflections of the Beckman beam test, compaction degrees and moisture contents. The correlation analysis indicates that both of two methods are suitable in rapid detecting subgrade performances, but PFWD method is more recommended for it has higher accuracy and efficiency.

Deterioration mechanism and rapid detection of performances of an existing subgrade in southern China


 Based on a highway reconstruction project in southern China, this study aims to put forward a method to determine the proper treatment depth of the existing subgrade. First, some field tests including the Beckman beam deflection test and portable falling weight deflectometer (PFWD) test were carried out. The results showed that there was a good correlation between the Beckman beam deflection (L) and PFWD modulus (Ep). Subsequently, a subgrade section was excavated and backfilled with cement-stabilized soil in layers. Compaction test, dynamic cone penetrometer rate test, plate load test and Beckman beam deflection test were performed to evaluate the treatment effect. To make sure, the subgrade was treated deeply enough, the Beckman beam deflection (L) was used as the controlled indicator among all the measured indexes for it was the hardest metric to meet. According to the design deflection and decreasing law of the measured deflections with the different number of the stabilized layers, the treatment depth was finally determined. As the PFWD test is superior to the deflection test in the detection efficiency, and the deflection value can be calculated from PFWD modulus by correlation formulas, thus the latter index can be used as a more suitable parameter for estimating the treatment depth instead of the former. Consequently, based on the measured PFWD moduli of the existing subgrade, six treatment schemes considering different treatment depths were proposed. It was confirmed that the method developed from this study is feasible and worth being extensively applied.

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Using portable falling weight deflectometer to determine treatment depth of subgrades in highway reconstruction of Southern China

In hot and humid regions of southern China, the volumetric moisture content of the embankment after opening to traffic for a period of time reaches a stable state, and it is higher than the design value. When it was widened, the humidity gradient and exchange were formed due to the difference in moisture content between the existing and new embankment. To reveal the moisture migration of the existing and new embankment and control the rise of volumetric moisture content in new embankment, six frequency domain reflectometry sensors were installed in existing and new embankment to monitor the volumetric moisture content. A finite element model for the embankment was established and verified with the measured data. And seven numerical analyses of transient seepage in the new embankment of the cushion, cover, and partition using capillary barrier by sand were simulated. The results show that the volumetric moisture contents of the new embankment in southern China gradually increase and eventually reach an equilibrium state. The increase in water comes from the slope, the foundation, and the existing embankment. Early in the first 1∼2 years, the water mainly comes from the foundation and the existing embankment. After that, as time goes by, the water comes mostly from the slope infiltration and gradually migrates to the foundation and the existing embankment. Finally, the volumetric moisture content and the water storage gradually reach equilibrium. The volumetric moisture content of the new embankment using capillary barrier by sand at the cushion, the cover, and the partition is maintained as the construction volumetric moisture content. This combination is a very effective method to control the humidity stability of the new embankment in southern China.

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Le Ding

Papers

Deterioration mechanism and rapid detection of performances of an existing subgrade in southern China

Using portable falling weight deflectometer to determine treatment depth of subgrades in highway reconstruction of Southern China

Moisture Migration and Control of New Embankment for Reconstruction and Expansion Project in Southern China