Zhengwu Jiang

Investigation on the potential of waste cooking oil as a grinding aid in Portland cement

Although there are several methods for managing waste cooking oil (WCO), a significant result has not been achieved in China. A new method is required for safe WCO management that minimizes the environmental threat. In this context, this work was developed in which cement clinker and gypsum were interground with various WCOs, and their properties, such as grindability, water-cement ratio required to achieve a normal consistency, setting times, compressive strength, contents of calcium hydroxide and ettringite in the hardened paste, microstructure and economic and environmental considerations, were addressed in detail. The results show that, overall, WCO favorably improves cement grinding. WCO prolonged the cement setting times and resulted in longer setting times. Additionally, more remarkable effects were found in cements in which WCO contained more unsaturated fatty acid. WCOs increased the cement strength. However, this enhancement was rated with respect to the WCO contents and components. WCOs decreased the CH and AFt contents in the cement hardened paste. Even the AFt content at later ages was reduced when WCO was used. WCO also densify microstructure of the hardened cement paste. It is economically and environmentally feasible to use WCOs as grinding aids in the cement grinding process. These results contribute to the application of WCOs as grinding aids and to the safe management of WCO.

Recent Advances in Intrinsic Self-Healing Cementitious Materials

Self-healing is a natural phenomenon whereby living organisms respond to damage. Recently, considerable research efforts have been invested in self-healing cementitious materials that are capable of restoring structural integrity and mechanical properties after being damaged. Inspired by nature, a variety of creative approaches are explored here based on the intrinsic or extrinsic healing mechanism. Research on new intrinsic self-healing cementitious materials with biomimetic features is on the forefront of material science, which provides a promising way to construct resilient and sustainable concrete infrastructures. Here, the current advances in the development of the intrinsic healing cementitious materials are described, and a new definition of intrinsic self-healing discussed. The methods to assess the efficiency of different healing mechanisms are briefly summarized. The critical insights are emphasized to guide the future research on the development of new self-healing cementitious materials.

Micromechanical framework for saturated concrete repaired by the electrochemical deposition method with interfacial transition zone effects

An improved micromechanical framework with interfacial transition zone (ITZ) effects is proposed for saturated concrete repaired by electrochemical deposition method (EDM) based on our recent studies. A multiphase micromechanical model with ITZs is proposed based on the material microstructure and a new multilevel homogenization scheme with inter-particle interactions is employed to predict the effective properties of repaired concrete considering the ITZ effects. The equivalent particle, composed by the water, deposition product and ITZ, is obtained by modifying the generalized self-consistent model. The mechanical properties of the healed concrete are calculated by micromechanical homogenization considering the inter-particle interactions. Moreover, modification procedures considering the ITZ effects are presented to attain the properties of repaired concrete in the dry state. To demonstrate the feasibility of the proposed micromechanical model, predictions in this study are compared with those of the existing models and the experimental data. Finally, the influences of ITZ on the equivalent particle and repaired concrete are discussed based on the proposed micromechanical framework.

Silicon carbide waste as a source of mixture materials for cement mortar

This paper presents an investigation of the feasibility of recycling silicon carbide waste (SCW) as a source of mixture materials in the production of cement mortar. Mortars with SCW were prepared by replacing different amounts of cement with SCW, and the properties of the resulting mortars, such as the fluidity, strength and shrinkage, were studied in this work. Thermogravimetry-differential scanning calorimetry and scanning electron microscopy were employed to understand the reasons for the property changes of the mortars. The results indicate that SCW decreases the initial and 1-h fluidity of fresh mortar but improves the loss of fluidity. The mortar with SCWexhibits a lower strength at 3 d and 7 d but a higher strength at 28 d and 56 d compared to the control. The shrinkage rate of cement mortar with SCW shows an obvious decrease as the replacement ratio increases. In addition, the content of calcium hydroxide in hardened paste also shows that SCW has some impact on the hydration of the cement-SCW system. The microstructures of the hardened paste also show evidence for a later strength change of mortar containing SCW. This work provides a strategic reference for possibly applying SCW as a mixture material in the production of cement mortar.

Stochastic micromechanical predictions for the effective properties of concrete considering the interfacial transition zone effects

A stochastic micromechanical framework for predicting the concrete probabilistic behavior is proposed considering the interfacial transition zone effects in this paper. The volume fraction of the interfacial transition zone is analytically calculated based on the aggregate grading. Multilevel homogenization schemes based on the direct interaction micromechanical solutions are presented to predict the concrete effective properties considering the aggregate and interfacial transition zone effects. By modeling the volume fractions and properties of the constituents as stochastic, we extend the deterministic framework to stochastic to incorporate the inherent randomness of effective properties among different concrete specimens. With the moments of the effective properties, the probability density function is approximated using the exponential polynomial for concrete material. Numerical examples including limited experimental validations, comparisons with existing micromechanical models, commonly used probability density functions, and the direct Monte Carlo simulations indicate that the proposed models provide an accurate and computationally efficient framework in characterizing the material’s effective properties. Finally, the effects of the randomness of interfacial transition zone and aggregate on the materials’ macroscopic probabilistic behaviors are investigated based on our proposed stochastic micromechanical framework.

Self-Shrinkage Behaviors of Waste Paper Fiber Reinforced Cement Paste considering Its Self-Curing Effect at Early-Ages

The aim of this paper was to study how the early-age self-shrinkage behavior of cement paste is affected by the addition of the waste paper fibers under sealed conditions. Although the primary focus was to determine whether the waste paper fibers are suitable to mitigate self-shrinkage as an internal curing agent under different adding ways, evaluating their strength, pore structure, and hydration properties provided further insight into the self-cured behavior of cement paste. Under the wet mixing condition, the waste paper fibers could mitigate the self-shrinkage of cement paste and, at additions of 0.2% by mass of cement, the waste paper fibers were found to show significant self-shrinkage cracking control while providing some internal curing. In addition, the self-curing efficiency results were analyzed based on the strength and the self-shrinkage behaviors of cement paste. Results indicated that, under a low water cement ratio, an optimal dosage and adding ways of the waste paper fibers could enhance the self-curing efficiency of cement paste.

An Experimental Study on the Repair of Deteriorated Concrete by the Electrochemical Deposition Method

Cracks significantly deteriorate the in-situ performance of concrete members and structures. Electrochemical deposition tests were performed to repair different types of damaged concrete specimens, such as specimen with the load-induced cracks and with the internal defects. Based on the authors’ previous work, electrochemical deposition tests are performed with the porous concrete specimens to assess its healing effects. Three kinds of experiments have been utilized to evaluate the deposition healing effectiveness. The experimental results show that the flexural strength improves after healing. The average ultrasonic pulse velocities increase from 3,546 m/s before healing, to 3,617 m/s after 14-day healing, to 3,656 m/s after 35-day healing, meanwhile the average porosities reduce from 0.2999, to 0.26245, and finally to 0.24092.

Migration and transformation of sulfur in the municipal sewage sludge during disposal in cement kiln

The aim of this work was to investigate the migration and transformation of sulfur in the municipal sewage sludge during disposal in cement kiln, and better understand the emission of the sulfur related pollutants in this process. In consideration of the temperature conditions in the practical operation, municipal sewage sludge was pre-dried at 105 °C, and then dried at 210, 260 and 310 °C, co-combusted with cement raw mill at 800, 900 and 1000 °C, and 1350, 1400 and 1450 °C respectively in the laboratory. X-ray photoelectron spectroscopy (XPS) was used to determine the S2p spectral lines of the municipal sewage sludge treated in the different process. Besides, The Thermal Analysis-Thermogravimetry (DTA-TG), Back Scattered Electron (BSE) and Energy Dispersive Spectrometer (EDS) were also employed to explore the mechanism of sulfur subsistence at 1450 °C. The results indicate that sulfide, thiophene, sulfone and sulfate are mainly sulfur compound in the municipal sewage sludge dried at 105 °C. Sulfoxide, a new sulfur compound, appears after it is further dried at 210 °C. The relative contents of sulfide and thiophene are continuously declined as the drying temperature increases due to their evaporation, decomposition and transformation in this process. The transformation of sulfide and thiophene makes the relative contents of sulfoxide and sulfate accordingly increased. However, the relative content of sulfone experiences an elevating-lowering process while the dry temperature elevated from 210 to 310 °C. This case is related to its evaporation and decomposition, as well as its production for the transformation of sulfide and thiophene. In the co-combustion process, sulfide, thiophene and sulfone are entirely vanished for their evaporation, decomposition and transformation. Sulfone is still contained at 800 °C, but when the temperature unceasingly rises, it is completely decomposed or evaporated and sulfate is the only sulfur compound. The microstructures left by the gas release are also observed in the mixtures sintered at 1450 °C, however sulfate still exists even at 1450 °C. The BSE and EDS results show that the melt phase is the important contribution to the appearance of sulfate at the high temperature. These results will sever as a theoretically reference for the pollution control of the sulfur related pollutants in the disposal process of the municipal sewage sludge in cement kiln.

Effect of Waste Paper Fiber on Properties of Cement-based Mortar and Relative Mechanism

The aim of this work was to investigate the effect of waste paper fiber on the properties of cement-based mortar and the relative mechanism. The cement-based mortars with various contents and mixing way of waste paper fibers were prepared and the slump flow, setting time and strength developments of all mortars were tested. Besides, Ca(OH)2 content in hardened pastes at different ages and the microstructures of all mortar at 90d were observed by scanning electron microscopy. The experimental results showed that in the process of mixing, more superplastizier was consumed to maintain the workability because of the absorption of water and superplastizer on waste paper fiber. With more waste paper fiber being added, longer setting time is available for the pastes with it because of the carbohydrate dissolving and its retarding to the cement hydration. Waste paper fiber is adverse to the early and later strength of cement-based mortar, but it increases the mortar strengths at 7 and 28 d. The strength, Ca(OH)2 content and microstructure are related to the content and mixing way of waste paper fiber. Waste paper fiber helps produce the Ca(OH)2 at 7 and 28 d, but this case is reverse at ages of 1 and 3 d. Overall, waste paper fiber leads to the appearance of more pores in the hardened paste. However, it increases the toughness of cement-based mortar.

A multiphase micromechanical model for unsaturated concrete repaired by electrochemical deposition method with the bonding effects

Most concrete structures repaired by the electrochemical deposition method are not fully saturated and the healing interfaces are not always perfect in reality. To demonstrate these issues, micromechanical models are presented for unsaturated concrete repaired by electrochemical deposition method with the healing interfacial transition zone based on our latest work. The repaired unsaturated concrete is represented as a multiphase composite made up of the water, unsaturated pores, intrinsic concrete, deposition products and the healing interfacial transition zone between the latter two components. The equivalent particle, matrix and composite for repaired unsaturated concrete are obtained by modifying the differential-scheme and the generalized self-consistent method. Modifications are utilized to rationalize the differential-scheme based estimations by taking into the water (including further hydration and viscosity effects), interfacial transition zone and the shapes of the pores into considerations. Furthermore, our predictions are compared with those of the existing models and available experimental results, thus illustrating the feasibility and capability of the proposed micromechanical framework.