This study aims to clarify the effects of curing regimes and lightweight aggregate(LWA)on the morphology, width and mechanical properties of the interfacial transition zone(ITZ) of ultra-high performance concrete(UHPC...This study aims to clarify the effects of curing regimes and lightweight aggregate(LWA)on the morphology, width and mechanical properties of the interfacial transition zone(ITZ) of ultra-high performance concrete(UHPC), and provide reference for the selection of lightweight ultra-high performance concrete(L-UHPC) curing regimes and the pre-wetting degree LWA. The results show that, under the three curing regimes(standard curing, steam curing and autoclaved curing), LWA is tightly bound to the matrix without obvious boundaries. ITZ width increases with the water absorption of LWA and decreases with increasing curing temperature. The ITZ microhardness is the highest when water absorption is 3%, and the microhardness value is more stable with the distance from LWA. Steam and autoclaved curing increase ITZ microhardness compared to standard curing. As LWA pre-wetting and curing temperatures increase, the degree of hydration at the ITZ increases, generating high-density CSH(HD CSH) and ultra-high-density CSH(UHD CSH), and reducing unhydrated particles in ITZ. ITZ micro-mechanical properties are optimized due to hydration products being denser.展开更多
Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement(cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under differen...Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement(cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under different curing regimes(standard curing, 90 ℃ steam curing, 200 ℃ and 250 ℃ autoclave curing) were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 ℃ steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement-quartz powder are C-S-H and CH. Under 200 or 250 ℃ autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.展开更多
Ethylene-Vinyl Acetate (EVA) redispersible powder and latex were used to modify mortar. Three kinds of curing regimes: standard curing, high temperature curing and freeze-thaw circle curing were adopted to cure the...Ethylene-Vinyl Acetate (EVA) redispersible powder and latex were used to modify mortar. Three kinds of curing regimes: standard curing, high temperature curing and freeze-thaw circle curing were adopted to cure the bonded samples. Bonding strength of EVA modified mortar was tested at 28 days. The development of bonding strengths under all three curing regimes were discussed and compared. The experimental results show that bonding strength increases with the increase of EVA content in mortar. The curing regime used within 28 days is critical according to the bonding strengths values under three curing regimes for different ages. The reasons of that the EVA can improve the bonding strength were analyzed.展开更多
基金Funded by the National Natural Science Foundation of China (Nos.U21A20149, 51878003, 51908378)Research Reserve of Anhui Jianzhu University (No.2022XMK01)Excellent Scientific Research and Innovation Team in Colleges and Universities of Anhui Province(No. 2022AH010017)。
文摘This study aims to clarify the effects of curing regimes and lightweight aggregate(LWA)on the morphology, width and mechanical properties of the interfacial transition zone(ITZ) of ultra-high performance concrete(UHPC), and provide reference for the selection of lightweight ultra-high performance concrete(L-UHPC) curing regimes and the pre-wetting degree LWA. The results show that, under the three curing regimes(standard curing, steam curing and autoclaved curing), LWA is tightly bound to the matrix without obvious boundaries. ITZ width increases with the water absorption of LWA and decreases with increasing curing temperature. The ITZ microhardness is the highest when water absorption is 3%, and the microhardness value is more stable with the distance from LWA. Steam and autoclaved curing increase ITZ microhardness compared to standard curing. As LWA pre-wetting and curing temperatures increase, the degree of hydration at the ITZ increases, generating high-density CSH(HD CSH) and ultra-high-density CSH(UHD CSH), and reducing unhydrated particles in ITZ. ITZ micro-mechanical properties are optimized due to hydration products being denser.
基金Funded by the National Natural Science Foundation of China(Nos.51272193,51372183,51072150)Program for New Century Excellent Talents in University(No.NCET-10-0660)the National Key Research Projects(No.2016YFB0303501)
文摘Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement(cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under different curing regimes(standard curing, 90 ℃ steam curing, 200 ℃ and 250 ℃ autoclave curing) were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 ℃ steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement-quartz powder are C-S-H and CH. Under 200 or 250 ℃ autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.
文摘Ethylene-Vinyl Acetate (EVA) redispersible powder and latex were used to modify mortar. Three kinds of curing regimes: standard curing, high temperature curing and freeze-thaw circle curing were adopted to cure the bonded samples. Bonding strength of EVA modified mortar was tested at 28 days. The development of bonding strengths under all three curing regimes were discussed and compared. The experimental results show that bonding strength increases with the increase of EVA content in mortar. The curing regime used within 28 days is critical according to the bonding strengths values under three curing regimes for different ages. The reasons of that the EVA can improve the bonding strength were analyzed.