Existing research on the mechanisms affecting the strength of cementitious materials primarily focuses on the composition and properties of cement hydration products, often overlooking the interactions between different products. This study presents a systematic experimental and theoretical investigation into the mechanical properties of cementitious materials, emphasizing the interactions between crystal and gel products driven by crystallization pressure. A new mechanism based on crystallization pressure is proposed to explain the impact of the interactions between hydration products on the strengths of cementitious materials. Experiments were conducted by immersing specimens in solutions with tailored ion concentrations (including water, isopropyl alcohol, ethanol, and solutions of calcium hydroxide and calcium acetate) to vary the crystallization pressure. The flexural and compressive strengths of these specimens were then tested. An analytical model was developed and validated against the experimental data. Both experimental and calculated results demonstrate a negative correlation between crystallization pressure and strength. Specimens subjected to crystallization pressures of 101.7 MPa and 147.8 MPa showed reductions in flexural strength of 19.34 % and 30.65 %, respectively, and decreases in compressive strength of 10.00 % and 14.41 %, compared to control specimens with zero crystallization pressure. These results suggest that ion concentrations in the pore solution alter the crystallization pressure, which in turn affects the interactions between crystal and gel products and strength of cementitious materials. This study provides insights into the mechanisms of strength degradation due to moisture in porous materials.

Upcycling of waste plastics into value-added chemicals and fuels represents a promising orientation toward a more sustainable chemical industry. We present a selective process for hydrocracking waste polyolefins into a spectrum of branched gasoline-range C_5-12 hydrocarbons, utilizing a cerium-promoted Pt/HY as a metal-acid bifunctional catalyst. The HY zeolite was engineered with a hierarchical meso/microporosity and moderated acidity to alleviate the overcracking of intermediate hydrocarbons to light C_1-4 gas products. The cerium presented as a surface cerium oxide phase, which mitigated acidity and significantly improved Pt dispersion. Upon a proper metal-acid balance, an optimized yield of C_5-12 up to 85 wt % was achieved from the low-density polyethylene over a cerium-promoted Pt/HY catalyst at 280 °C and 2 MPa H₂ for 2 h. The tandem catalysis was proposed to proceed with an initial dehydrogenation of the polymer chain over Pt sites, with subsequent isomerization and cracking over the Brønsted acid sites and hydrogenation of the olefin intermediates over Pt sites. The strong Pt-O-Ce bridging structure inhibited the migration and agglomeration of Pt atoms, affording good stability and no distinct performance loss over three sequential runs. This process is applicable to the hydrocracking of other polyolefins such as high-density polyethylene, polypropylene, and daily plastic bags to gasoline-range fuels in desirable yields (60-80 wt %).

The potential crisis of phosphorus resource is unprecedentedly pushing phosphorus recovery from wastewater and other sources. Although products of phosphorus recovery are variable, economic and high value-added products could promote owners to do so voluntarily. Among others, vivianite (Fe ₃ (PO ₄ ) ₂ •8H ₂ O), which has been found to exist largely during biological sludge (biomass), is arousing attention to researchers. In fact, vivianite, a stable (K _sp = 10 ^-36 ) ferrophosphorus compound, widely exists in natural sediments. Besides such inherent factors as rich iron and phosphate, there are also some external factors determining formation of vivianite, like low oxidation-reduction potentials (ORP<-300 mV) and suitable pH conditions (6~9), etc. Fortunately, these inherent and external factors could be satisfied in wastewater and/or processes of wastewater treatment, and some wastewater treatment plants (WWTPs) in the Netherlands declared that they indeed found a large amount of vivianite presence in biological sludge. To promote both fundamental and applied researches on vivianite, the article reviews vivianite in: i) chemical properties, economic value and recovered potential; ii)controlling factors like pH, ORP, microorganisms, sulfide, etc.; iii) pathways of vivianite formation in biological sludge; iv) separation and purification of vivianite.

One of the key parameters for the performance of concrete repairs is the quality of the interface between repair material and concrete substrate. To understand the properties of the interface in concrete repairs with cementitious repair materials, cement hydration and microstructure were experimentally studied using non-evaporable water test, mercury intrusion porosimetry, and scanning electron microscopy techniques. The experimental results reveal that the moisture exchange between repair material and concrete substrate results in a change of the moisture content in the repair material and thus affects the cement hydration process and pore structure development. Backscattered electron images demonstrate the existence of an interfacial transition zone of high porosity, since the cement particles of the repair material have a poor packing on the surface of concrete substrate.