Zichen Lu

The varied damage faced by concrete in the pavement can be effectively alleviated by adding polymer latex. However, their required high dosage and prices limit their application. Hence, a new structure with the gradient distribution of polymer particles in concrete was designed. Furthermore, the performance and the corresponding mechanism of varied polymer types and contents on the mechanical performance of polymer‐modified mortar (PMM) were systematically evaluated. Compared to the sample with a homogenous polymer distribution at the same dosage, a great enhancement in compressive and bond strength was found for PMM with the gradient structure. Besides, the flexural strength can also be slightly increased. Compared to styrene‐acrylic (SA) and ethylene‐vinyl acetate (EVA) latexes, styrene‐butadiene (SB) latex with the highest charge density shows the lowest capability in modifying the mechanical performance of PMM, which could be caused by its high adsorption amount and low ductility of formed polymer film. It further indicates that, compared to the tensile stress of polymer film, its ductility is more important in determining the flexural strength of PMM. To confirm the obtained experimental results, a finite element model of mortars with different gradient structures was established, and the modeling results match well with the mechanical measurements.

Effect of aging conditions on the hydration and setting performance of cement paste with the addition of TEA were investigated through the combined techniques of calorimetry, Vicat test, XRD and TGA. It is found that, along with the increased aging time and RH, an obvious formation of AFt, AFm and CH can be found due to the pre-hydration of clinker. Besides, under the RH of 90%, the pre-hydration within the first day was significantly improved, and this process was continuously developed in the next 7 days through the strong carbonation of CH. Further analysis indicates that the pre-hydration can retard the cement hydration and increase the setting time of cement paste. Compared to the reference, a prolonged induction period and an increased setting time were observed for the aged samples with the addition of TEA. Besides, the commonly observed flash setting performance under the TEA dosage of 0.5 wt.-% was eliminated when the samples were pre-hydrated under 90% RH, which indicates the pre-hydration can alleviate the strongly accelerated aluminate phase hydration caused by TEA.

The feasibility and performance of using calcined coal gangue (CCG) to substitute metakaolin (MK) as the precursor to prepare alkali-activated materials (AAMs) were thoroughly evaluated by conducting combined experiments of flowability test, mechanical measurement, calorimetry and microstructure analysis, etc. It was found that the increased substitution ratio of CCG to MK can increase the flowability of the prepared paste by up to 28.1% and decrease its viscosity by up to 55.8%. In addition, a prolonged setting time of up to 31.8% was found with the increased substitution amount of CCG to MK, which can be attributed to the low reactivity of CCG compared to that of MK. Lastly, even though the presence of CCG can lead to a decrease in the early compressive strength of the hardened paste, a highly recovered long-term mechanical property can be found due to the continuous reaction of CCG. All of these results prove the feasibility of using CCG as one co-blended precursor with MK to prepare alkali-activated materials.