Sustainable Use of Sludge from Industrial Park Wastewater Treatment Plants in Manufacturing Lightweight Aggregates

Evaluation of the Superiority of Lightweight-Aggregate-Concrete Prestressed Box Girders in Terms of Durability and Prestress Loss

This case study aimed to compare the differences in the durability and prestress loss between normal-weight-concrete (NC) and lightweight-aggregate-concrete (LWC) prestressed box girders, which were constructed at the same time in the same area, so as to verify the superiority of using synthetic lightweight aggregate (LWA) made from reservoir sediments in prestressed bridges. For the NCs and LWCs used in the prestressed box girders, the basic mechanical properties (compressive strength, flexural strength, splitting tensile strength, and elastic modulus) were tested, as well as the durability properties (chloride ion penetration resistance and rapid chloride permeability). Then, through the prestress-monitoring system, the prestress losses of the two groups of prestressed box girders were tracked. The results of the durability test confirmed that LWC can inhibit the penetration of air, water, and chloride ions by strengthening the interfacial transition zone between the aggregate and the cement paste, thereby improving its durability. Moreover, the magnetic-flux prestress loss of the NC prestressed box girder reached 8.1%. In contrast, the magnetic-flux prestress losses on both sides of the LWC prestressed box girder were 4.6% and 4.9%, respectively. This verified that, under the same environmental conditions, the use of LWC produced less of a prestress loss than the use of NC.

Assessment of Dynamic Surface Leaching of Monolithic Polymer Mortars Comprised of Wastes

Today, the reuse of waste in building materials occupies an important place in the approach to the circularity of materials. National and European environmental regulations require ensuring the environmental safety of material-incorporating waste. For this, there are specific tests to verify that there is no health risk when using these materials. Concretely, to check the environmental acceptability of construction materials, including wastes, the release of hazardous substances into water must be assessed. In this research, we performed a diffusion test with the sequential renewal of water during a 64-day period according to the NF EN 15863 specifications on polymer mortar monoliths, common construction products used in floor-covering applications and incorporating sediments. Polymer mortars were prepared at a laboratory scale by incorporating 30 or 50% of polluted sediment for various polymer concentrations (12, 14, 16, 18, 20 and 25%). It was shown that the release of inorganic substances is limited in these hydrodynamic conditions. Among trace elements, As, Cd, Cr, Ni, Pb and Zn are lower than quantification limits in most leachates, whereas Ba, Co, Cu and V are systematically quantified at low concentration levels. This is particularly true for samples displaying the highest polymer concentration (25%) and the lowest sediment incorporation rate (30%). This is because of the low water absorption level and low porosity of polymer mortar matrices. No adverse effect is to be expected for environmental health from the leachates of these construction materials, including waterways sediments, because all the measured parameters were below the Soil Quality Decree limits applied in the Netherlands for environmental assessment of construction products.

The Corrosion Resistance of Reinforced Lightweight Aggregate Concrete in Strong Brine Environments

Taiwan has used technology in reservoir sediments and industrial waste to produce high-performance lightweight aggregate (LWA). LWA can be used to manufacture lightweight aggregate concrete (LWAC) with structural strength ratings. At present, Taiwan's offshore wind turbines are gradually developing and are moving from coastal areas to deep-sea areas. With this in mind, this study aimed to investigate the feasibility of applying LWAC with synthetic LWA from reservoir sediments to floating offshore wind turbine foundations. LWAC and normal-weight concretes (NWC) of different strengths were prepared, and their fresh, hardened, and durability properties were tested. In addition, reinforced concrete and steel sheets were immersed in a tank of high salinity seawater to examine their resistance to seawater-accelerated corrosion. The test results showed that the total passing charge of the two groups of concrete within six hours was less than 1000 coulombs. Both groups of concrete were classified as having "Very Low" chloride permeability. The average corrosion potential of most reinforced concrete specimens was found to be greater than -200 mV, which means that the corrosion probability of the steel bars was less than 10%. Furthermore, the use of coatings for seawater corrosion protection on steel sheets was not found to be as effective as reinforced concrete. This shows that the use of LWAC with synthetic LWA from reservoir sediments for the floating foundations of offshore wind turbines is feasible and has design flexibility.