Construction Materials: Characterization, Structure and Durability

The objective of this work was the study of four experimental plastic covers (EPCs) to assess the improvement in microclimatic conditions inside a greenhouse. This experiment was based on the comparison of four trilayer plastics: blue, grey, yellow and colorless ECPs. Radiometric and mechanical properties were studied along with the films’ behavior under semi-field conditions through their microclimate parameters. The results show that the addition of the blue pigment causes a considerable reduction in transmission (32.04%) with a reduction in the maximum temperature (+9.8 °C) compared to the other films (14% for grey, 52% for yellow and 46% for colorless). The anti-thermal additive used in the grey EPC did not achieve the desired effect, since it reduced both the photosynthetic active radiation (PAR) (62.33%) and near-infrared radiation (NIR) (62.83%) transmission equally. None of the EPCs achieved a PAR/NIR ratio greater than 1 (0.52 for blue, 0.99 for grey, 0.98 for yellow and 0.99 for colorless). Hindered amine light stabilizers (HALSs) photo-stabilizing additives block UV-A radiation (36.85 for grey) more efficiently compared to nickel quenchers (38.64 for yellow), as they allow earlier PAR transmission. The tensile test showed that all the EPCs manifested a linear relationship between stress and deformation, which defines Young’s modulus. Full article

The inhomogeneous settlement of subgrade seriously affects the safety of aircraft operation. To investigate the mechanical response of pavement slabs supported on an inhomogeneous settlement, a three-dimensional model of aircraft load–pavement structure–heterogeneous pavement was established; then, the inhomogeneous settlement conditions were simulated by setting a different reaction modulus between adjacent subgrades. Finally, both numerical simulation and experimental study methods were used to analyze the flexural tensile stress and vertical displacement of the pavement slab in inhomogeneous settlement conditions under the loading effects of typical aircrafts (A320 and B737-800). The results indicate that the strain of pavement slabs increases as the change rate of an inhomogeneous subgrade support increases. Increasing the thickness of the pavement slab and reducing the inhomogeneous subgrade support can effectively improve the mechanical performance of the pavement structure. For B737-800, with the change rate of the inhomogeneous subgrade support increasing from 0% to 85.71%, the amplitude of the flexural tensile stress of the pavement slab increased by 34%. The pavement slab with a thickness of 0.36 m experienced flexural–tensile failure. For pavement slabs with thicknesses of 0.38 m and 0.40 m, the maximum inhomogeneity of the subgrade roof support should not exceed 33% or 62%, respectively. Therefore, the effect of the horizontal inhomogeneous subgrade support caused by long-term environmental action should be considered when designing pavement slabs. Full article

The paper presents the results of testing the performance of lightweight structural concrete containing hemp shives as an aggregate. It has been analysed how the higher binder content and use of the Portland cement affect the thermal and microbiological properties of the lightweight concrete. The aggregates of the plant origin and cement are incompatible because the plant chemical compounds, dissolved in water or an alkaline environment, inhibit cement hydration. To avoid this, mineralisation of the aggregates of plant origin is necessary. The most often used binder in hemp concrete is hydrated lime, a mineraliser. An addition of hydrated lime and sodium trisilicate was used for hemp shiv mineralisation in the tested materials with a cement binder. Concrete containing hemp shiv and cement binder, of which volume share in the concrete was at most 15%, was prepared as a reference concrete. In the remaining three concretes, the total content of the binder in relation to hemp shiv (by mass) was increased 2.5 times. It was shown that lime-binder hemp concrete offers a promising antimicrobial strategy, as it can inhibit bacterial and fungal growth on their surface with superior efficacy. The best results were obtained for tested concretes with the cement–lime binder regarding compressive strength; the average compressive strength was 9.56 MPa. Full article

In this paper, mixtures with different proportions of lime, phosphogypsum, and red clay were prepared, and the road properties and micromechanisms of lime–phosphogypsum-stabilized red clay were investigated by unconfined compressive strength test, water stability test, swelling test, shrinkage test, XRD quantitative analysis, and scanning electron microscope analysis. The results showed that the unconfined compressive strength of the mix increased and then decreased with the increase of phosphogypsum content. With the increase of age, the growth was faster in the first 14 days and basically stabilized in the last 14 days. The mixture has poor water stability, large absolute swelling rate, and low linear shrinkage. The reason for the increase of strength is that the reaction of lime, phosphogypsum, and red clay produces ettringite, and the cementing substance gels form a three-dimensional mesh skeleton structure; the excess of ettringite will cause the skeleton to expand and break, and the strength decreases. Full article

The backfilling of lime soil in ultra-deep and ultra-narrow foundation trenches is a difficult construction link, and ordinary-cemented soil has drawbacks, including poor strength, impermeability, and frost resistance. To solve these problems, fly ash (FA)–water glass (WG)-composite-cemented soil is developed based on a background project. The three-factor orthogonal tests are conducted on the unconfined compressive strength (UCS) of the composite-cemented soil, and the optimal engineering mix proportion is proposed for the FA-WG-composite-cemented soil. Its UCS is compared with that of cemented soil only doped with FA or WG (FA- and WG-cemented soil). In addition, the cyclic wetting–drying tests, cyclic freeze–thaw tests, and impermeability tests are carried out to study the endurance of the composite-cemented soil in cold regions rich in water. The hydration products of the composite-cemented soil are investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, and the curing mechanism of the composite-cemented soil is discussed from the microscopic perspective. The research results indicate that the mixing ratio of cement is crucial to the strength development of the cemented soil; the mixing ratio of FA greatly influences the strength development of the cemented soil in the middle and late stages; the mixing ratio of WG only slightly affects the strength. The ratio of cement, FA, and WG of 9%:12%:3% is the optimal engineering mix proportion of the composite-cemented soil. Compared with ordinary-cemented oil and FA- and WG-cemented soil, the composite-cemented soil shows significantly improved compressive load-bearing capacity. The permeability coefficient of the composite-cemented soil is always obviously lower than that of the ordinary-cemented soil after any curing period. Despite the mass loss, the composite-cemented soil is superior to the ordinary one in overall endurance after wetting–drying and freeze–thaw cycles. Through SEM and XRD analysis, the content of hydration products of the composite-cemented soil is found to be obviously higher than that of ordinary-cemented soil after any curing period, and the hydrates exert stronger cementing action on soil particles in the composite-cemented soil. The contents of C-S-H gel and Aft crystals in the composite-cemented soil are apparently larger than those in the ordinary-cemented soil. Under the alkali activation of WG, the FA produces free SiO₃²⁻ and AlO²⁻, which undergo the polymerization reaction with Ca²⁺ to generate C-S-H gel and C-A-H gel, further promoting the hydration of cement. Full article

Polyurethane cement composite is a new organic–inorganic composite material with high strength, corrosion resistance, and fast curing. It is a complement and alternative to traditional cement materials. The flexural properties of polyurethane cement composites are the basic mechanical index of the material. In order to study the flexural properties under different temperature loads, a molecular model was established, the chemical reaction process of polyurethane cement and the temperature response mechanism was analyzed, and the preparation process of polyurethane cement was proposed. Then, bending tests were carried out in strain-controlled mode to obtain the specimens’ bending strength and stiffness modulus under different temperature loads. The test results showed that the tensile strength of polyurethane cement decreased first, then increased, and finally decreased with the increase in temperature, while the bending stiffness modulus decreased with the increase in temperature. Combined with the theoretical derivation, the damage mode of the samples under different temperature loads was analyzed, and the “L-type” damage strain curve was obtained. The results showed that the proposed theory could effectively explain the mechanism of action and flexural properties of polyurethane cement composites under temperature loading, which is a significant improvement to the application of polyurethane cement composites in practical engineering. Full article

The advancement of marine engineering has brought close attention to the durability of concrete structures. In order to investigate the time-varying performance of reinforced concrete beams in a marine environment and to better apply sea sand directly in marine engineering, this paper describes tests and analysis on the flexural performance of reinforced sea sand concrete beams after being exposed to a tidal environment. Eight beams were tested using four-point static loading equipment. The variation parameters included the type of mixing water, longitudinal reinforcement rate, sea sand replacement rate and duration of service. The force damage process and damage pattern were observed. The load–maximum width crack curve and load–deflection curve were obtained. The effects of each variation parameter on the mechanical properties such as ultimate bearing capacity, initial rigidity, energy dissipation coefficient and ductility coefficient were analyzed. The test results show that compared with the specimens exposed to the tidal environment for 90 days, the peak load of the specimens decreased by 5.6%, the initial rigidity decreased by 60.9% and the ductility coefficient decreased by 41% after 270 days of exposure, while the peak deflection and energy dissipation indexes first increased and then decreased. The seawater mixing can enhance the peak load and cracking load of the specimens, but the initial rigidity, peak deflection, energy dissipation coefficient and ductility coefficient of the specimens are reduced to some extent. The initial rigidity of the specimens tended to increase with the increase in the sea sand replacement, but the peak load decreased. Under the same reinforcement rate, reducing the diameter of the reinforcement is beneficial to improve the initial rigidity of the specimen, while using the reinforcement with higher elongation can effectively enhance the peak deflection of the specimen. Based on the Chinese code, the calculation method of flexural bearing capacity with modified concrete strength is proposed, and the calculation results are in good agreement with the test results. Full article

Fourier-transform infrared (FTIR) spectroscopy is a fast and simple technique for functional group identification. This work provides a review and insight into the application and interpretation of FTIR spectroscopy for cementitious binders that comprise ordinary Portland cement, alkaline-activated binders, geopolymers, and material characterization for civil engineering material applications. This technique can be used to identify different compounds and a moiety of bond vibrations in inorganic molecules such as Si-O, -OH, H-O-H (water), C-O (carbonate or carbonation), aluminosilicate (Si-O-T, where T is Al or Si), and S-O (sulfate or gypsum) found in hydrated cement, alkaline binders, and geopolymers. The prominent bands include those representing carbonation (CO₃²⁻ 1390–1475 cm⁻¹), calcium carbonate (871, 1792–2516 cm⁻¹), hydroxylation and water molecules (1607, 3400–3650 cm⁻¹), strength skeletal framework compositions or Al-Si substitutions, silicate organization (C-A-S-H, N-A-S-H, or C-S-H (950–1055 cm⁻¹), and sulfate (600–680, 1080–1100 cm⁻¹). Some of the factors that could affect the spectra bands include elemental displacement due to changes in molar mass, activated temperature, pH, activator concentration, w/b ratio, Ca/Si ratio, Si/Al ratio, and the silica modulus (SiO₂/Na₂O) of the activators used in the binder synthesis. The method could be used for destructive and non-destructive testing on paste sample by using transmission and attenuated total reflectance methods, respectively. Full article