Microcapsule-Type Self-Healing Protective Coating That Can Maintain Its Healed State upon Crack Expansion

The purpose of this study was to develop a microcapsule-type self-healing coating system that could self-heal cracks and then maintain the healed state even upon crack expansion. Mixtures consisting of a photoinitiator and two methacrylate components, bismethacryloxypropyl-terminated polydimethylsiloxane (BMT-PDMS) and monomethacryloxypropyl-terminated PDMS (MMT-PDMS), were transformed into viscoelastic semi-solids through photoreaction. The viscoelasticity of the reacted mixtures could be controlled by varying the mass ratio of the two methacrylates. Through a stretchability test, the optimal composition mixture was chosen as a healing agent. Microcapsules loaded with the healing agent were prepared and dispersed in a commercial undercoating to obtain a self-healing coating formulation. The formulation was applied onto mortar specimens, and then cracks were generated in the coating by using a universal testing machine (UTM). Cracks with around a 150-μm mean width were generated and were allowed to self-heal under UV light. Then, the cracks were expanded up to 650 μm in width. By conducting a water sorptivity test at each expanded crack width, the self-healing efficiency and capability of maintaining the healed state were evaluated. The B-M-1.5-1-based coating showed a healing efficiency of 90% at a 150-μm crack width and maintained its healing efficiency (about 80%) up to a 350-μm crack width. This self-healing coating system is promising for the protection of structural materials that can undergo crack formation and expansion.

Soil water repellency influences maize yield by changing soil water availability under long-term tillage management

Drought is increasingly common due to frequent occurrences of extreme weather events, which further increases soil water repellency (SWR) and influences grain yield. Conservation agriculture is playing a vital role in attaining high food security and it could also increase SWR. However, the relationship between SWR and grain yield under conservation agriculture is still not fully understood. We studied the impact of SWR in 0–5 cm, 5–10 cm, and 10–20 cm layers during three growth periods on grain yield from a soil water availability perspective using a long-term field experiment. In particular, we assessed the effect of SWR on soil water content under two rainfall events with different rainfall intensities. Three treatments were conducted: conventional tillage (CT), reduced tillage (RT), and no-tillage (NT). The results showed that the water repellency index (RI) of NT and RT treatments in 0–20 cm layers was increased by 12.9 %–39.9 % and 5.7 %–18.2 % compared to CT treatment during the three growth periods, respectively. The effect of the RI on soil water content became more obvious with the decrease in soil moisture following rainfall, which was also influenced by rainfall intensity. The RI played a prominent role in increasing soil water storage during the three growth periods compared to the soil total porosity, penetration resistance, mean weight diameter, and organic carbon content. Furthermore, although the increment in the RI under NT treatment increased the soil water storage, grain yield was not influenced by RI (p > 0.05) because the grain yield under NT treatment was mainly driven by penetration resistance and least limiting water range (LLWR). The higher water sorptivity increased LLWR and water use efficiency, which further increased the grain yield under RT treatment. Overall, SWR, which was characterized by water sorptivity and RI, had the potential to influence grain yield by changing soil water availability (e.g. LLWR and soil water storage) and RT treatment was the most effective tillage management compared to CT and NT treatments in improving grain yield.

Using of recycled clay brick/fine soil to produce sodium hydroxide alkali activated mortars

In the study, the recycled clay brick powder/fine soil powder-based sodium hydroxide alkali-activated mortar (AAM) specimens were prepared by mixing different percentages (100/0, 80/20, 60/40, 40/60, 20/80, and 100/0, respectively) to investigate the mechanical and durability performance of sustainable AAM specimens for the possible utilization instead of OPC. The constant ratio of glass powder was used in the production of AAM to increase the alkalinity and improve the mechanical properties of alkali-activated mortar. Also, the influences of sodium hydroxide molarity concentrations (8, 10, 12, 14, and 16 M) on the performance of AAM specimens were studied. The compressive strength, water absorption, and water sorptivity tests were conducted on the AAM specimens and the relationships between the investigated parameters were analyzed. The obtained results revealed that the fine soil powder replacement with clay brick powder improved the compressive strength, and reduced water absorption and water sorptivity up to 80% replacement ratios, and the superior mechanical and durability performance was obtained in the 80% fine soil powder-based AAM specimens. For the higher fine soil powder replacement ratio (100%), the performances of the AAM specimens were found to be adversely affected. Besides, the concentration of NaOH solution significantly influenced the material performances of the fine soil powder-based AAMs and 12 M NaOH concentration performed superior mechanical and durability performance. The strength enhancement of the AAMs was found to be significant after 90 days of ambient curing period.

A critical review of the Water Sorptivity Index (WSI) parameter for potential durability assessment: Can WSI be considered in isolation of porosity?

ABSTRACT The Durability Index (DI) approach used in South Africa is linked to transport-related properties of the cover layer of concrete. This performance-based approach utilises three different durability-related parameters, namely Water Sorptivity Index (WSI), Oxygen Permeability Index (OPI) and Chloride Conductivity Index (CCI). In the water sorptivity test, both the sorptivity and the water-penetrable porosity of the concrete are measured. Until now, porosity has not been considered directly as a separate durability-related parameter. This paper analyses these implications and suggests that porosity should be adopted as a further index. The paper concludes that sorptivity cannot be interpreted without also reflecting the porosity value since these two parameters are inter-related. Keywords: concrete durability, durability index, water sorptivity, porosity, absorption

Utilization of Drinking Water Treatment Sludge as Cement Replacement to Mitigate Alkali–Silica Reaction in Cement Composites

Alkali–silica reaction (ASR) attack is one of the most significant durability concerns in cement-based materials. In this paper, the drinking water treatment sludge (DWTS), which is a typical by-product from the drinking water treatment industry, was reused as supplementary cementitious material to mitigate the degradation of mortar resulting from ASR attack. DWTS was milled and calcined at 800 °C for 2 h before being used as a replacement for cement. Glass sand was used as the reactive fine aggregate. Properties of four mortar mixtures prepared with 0%, 5%, 10%, and 20% of calcined DWTS replacement of cement were firstly assessed, including compressive strength, flexural strength, and water sorptivity. The mortar specimens were then exposed to an ASR-attacked environment for 28 days, the changes in specimen length were monitored, and the uniformity of mortar was measured via Ultrasonic pulse velocity (UPV). The results showed that 10% replacement significantly improved the mechanical properties of mortar. The specimens with 20% of the calcined DWTS exhibited comparable strength relative to the reference group and exhibited superior resistance to ASR attack. Additionally, a water sorptivity test showed that higher contents of the calcined DWTS can lead to lower water capillary absorption of mortar.

Effect of secondary succession in abandoned fields on some properties of acidic sandy soils

<p>Abandonment of agricultural lands in recent decades is occurring mainly in Europe, North America and Oceania, and changing the fate of landscapes as the ecosystem recovers during fallow stage. The objective of this study was to find the impact of secondary succession in abandoned fields on some parameters of acidic sandy soils in the Borská nížina lowland (southwestern Slovakia). We investigated soil chemical (pH and soil organic carbon content), hydrophysical (water sorptivity, and hydraulic conductivity), and water repellency (water drop penetration time, water repellency cessation time, repellency index, and modified repellency index) parameters, as well as the ethanol sorptivity of the studied soils. Both the hydrophysical and chemical parameters decreased significantly during abandonment of the three investigated agricultural fields. On the other hand, the water repellency parameters increased significantly, but the ethanol sorptivity did not change during abandonment. As the ethanol sorptivity depends mainly on soil pore size, the last finding could mean that the pore size of acidic sandy soils did not change during succession.</p>