Polyethylene (PE) is an important polymeric material which is widely used in civil engineering. Recently, engineered cementitious composites (ECCs) have adopted PE fibers in structural repairing. ECC with polyethylene fibers (PE-ECC) has excellent tensile properties, ductility, strain-hardening behavior, thermal performance and durability. In this paper, a systematic review of the cementitious composites with PE fibers is summarized to facilitate the application of PE-ECC. The influence of PE fibers on the properties of ECC, such as compressive strength, flexural behavior, shear properties, impact resistance and tensile properties, is presented. Meanwhile, the properties of PE-ECC repaired structures, such as beams, walls and columns, are described. Further, the self-repairing properties of PE-ECC are presented. Finally, some suggestions for future research are provided in order to apply PE-ECC to practical repairing cases. The review exhibits that PE-ECC is of notable significance to the repairing of structures and clarifies its application scope.

Cementitious composites with microencapsulated healing agents are appealing due to the advantages of self-healing. The polymeric shell and polymeric healing agents in microcapsules have been proven effective in self-healing, while these microcapsules decrease the effective elastic properties of cementitious composites before self-healing happens. The reduction of effective elastic properties can be evaluated by micromechanics. The substantial complicacy included in micromechanical models leads to the need of specifying a large number of parameters and inputs. Meanwhile, there are nonlinearities in input–output relationships. Hence, it is a prerequisite to know the sensitivity of the models. A micromechanical model which can evaluate the effective properties of the microcapsule-contained cementitious material is proposed. Subsequently, a quantitative global sensitivity analysis technique, the Extended Fourier Amplitude Sensitivity Test (EFAST), is applied to identify which parameters are required for knowledge improvement to achieve the desired level of confidence in the results. Sensitivity indices for first-order effects are computed. Results show the volume fraction of microcapsules is the most important factor which influences the effective properties of self-healing cementitious composites before self-healing. The influence of interfacial properties cannot be neglected. The research sheds new light on the influence of parameters on microcapsule-contained self-healing composites.

The objective of this paper is to investigate the coupling effect of cement and organosilicon hydrophobic agents on the water resistance of phosphogypsum. Different weight ratios of Portland cement were added to adjust the alkalinity of this system and further improve the work efficiency of the organosilicon hydrophobic agents. Some macroscopic performances, such as the water absorption, the compressive strength, the flexural strength, and the softening coefficient, were measured to characterize the water-resistance of phosphogypsum. The microscopic characteristics were analyzed via contact angle tests, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to understand the mechanism of organosilicon hydrophobicity. The results indicated that both the compressive and flexural strengths of phosphogypsum first increased and then decreased with the increase of organosilicon hydrophobic agents. Meanwhile, the surface contact angle continued to increase and the softening coefficient exhibited an obvious increase. When the hydrophobic agent was combined with Portland cement, the softening coefficient of phosphogypsum further increased from 0.80 to 0.99, while the water absorption rate was significantly reduced from 16.0% to 0.8%. Microscopic tests proved that the hydrophobic organic molecules can be polymerized under the high alkalinity, and promote the formation of a hydrophobic film, thus significantly improving the water-resistance of phosphogypsum.

Carbon fiber dispersion has a substantial influence on the properties of amorphous calcium silicate hydrate-based contact-hardening composites. In this study, a mixture of carbon fiber and calcium silicate hydrate powder was compressed into solid composites at 40 MPa for one minute. The mechanical properties and electrical resistivity of the solid materials were measured, and the dispersion of carbon fibers was quantitatively evaluated by digital image processing technology. The Taipalu model was used to build the correlation between the electrical resistivity of the composites and the carbon fiber dispersion. The results of the electrical resistivity showed that the down threshold of carbon fiber content in the contact-hardening composites was 1.0 wt.% and the electrical resistivity was 30,000 Ω·cm. As the fiber content increased to 2.0 wt.%, the electrical resistivity dropped to 2550 Ω·cm, which was attributed to the increase in fiber dispersion uniformity in the solid composites, and the value of the fiber distribution coefficient reached a maximum value of 0.743. A subsequent decrease in the uniformity of the fiber dispersion was observed at a high fiber content. In addition, the carbon fiber content showed a slight influence on the fiber orientation in the contact-hardening composites.

This paper presents a study on sulfate resistance of mortars blended with and without silica fume or fly ash under electrical field. Performance of the mortars was determined by various means such as visual examination, sulfate concentration, flexural and compressive strength, as well as mineralogical analysis. The results showed that electrical field accelerated the deterioration induced by sulfate attack, as it sped up the ingress of sulfate ions into the mortar. The use of mineral admixtures improved the sulfate resistance of mortars. However, a relatively great amount of migrated sulfate as well as expansive sulfate products (gypsum and ettringite) were still found in the blended cement mortars under the electrical field, for which their deterioration was also notable. Therefore, the electrical field also accelerated sulfate attack on the mortars blended with mineral admixtures.

To address the potential adverse impact of silane on cement hydration, this study systematically investigates the effects of power ultrasound on the mechanical and hydrophobic properties, and the microstructure of silane-modified cement paste. Experimental results showed that ultrasonic treatment within the 240-720 W range significantly enhanced the compressive strength compared to the reference group. In particular, the 480 W group exhibited increases in compressive strength of 36.9 %, 10.7 %, and 7.9 % at 1, 3, and 28 days, respectively. X-ray diffraction and TG analysis revealed that this treatment accelerated the dissolution and hydration degree of the clinker. Contact angle measurements indicated that optimal hydrophobic performance was achieved at 720 W, with a contact angle of 133.0°, representing a 34.2 % increase compared to the reference group. These findings indicate that power ultrasound holds excellent potential for preparing the hydrophobic cementitious materials.