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In the present work, the synergetic effect of fly ash (FA) and ground granulated blast furnace slag (GGBS) on the compressive strength and microstructure development of mortars subjected to CO 2 curing coupled with further water curing was investigated. The calcite content in pure cement was first increased and then decreased, while it decreased gradually in cement incorporating FA and GGBS during further water curing. Ettringite was interlocked with calcium carbonate and MC and was only observed in pure cement paste. Two distinct forms of C–S–H were observed in pure cement with one being interlocked with calcite, while the other one was pure amorphous phase. The incorporation of FA and GGBS showed a negative effect on the polymerization decrease of silica-rich phase. FA showed a negligible effect on the decrease of porosity, while GGBS had a positive effect on it. A positive correlation was found between the increase of compressive strength subsequent to water curing and three parameters, i.e., crystal size of calcite, carbonation degree and capillary pore percentage after CO 2 curing, where the carbonation degree had a negative effect, while the other two parameters had a positive effect. The incorporation of GGBS and FA had a positive effect on the strength increase rate during further water curing. Notably, GGBS showed a more obvious effect on the strength development during further water curing and normal curing at later age. When GGBS content was lower than 10 % or cement content was lower than 10 %, the increase of FA content had a positive effect on the strength increase. [ABSTRACT FROM AUTHOR]

This study investigated the effect of wet carbonated recycled cement paste powder (RCPP) on the rheological properties of cement pastes. The results showed that wet carbonated RCPP decreased the cement paste's setting time and flowability, increased its yield stress and plastic viscosity, and changed its thixotropy. The high absorption capacity of the silica gel in the carbonated RCPP was the most dominant factor influencing the rheological properties of the paste. The absorption capacity of silica gel was dependent on its pore structure, specific surface area, and the amount of hydroxyl groups on its surface. These properties varied with the carbonation method, time, temperature, and CO 2 flow rate. The use of monoethanolamine as the aqueous solution for wet carbonation was found to be an effective approach to mitigate the adverse effect of carbonated RCPP on the rheological properties of cement paste. • Carbonated recycled cement paste powder deteriorated the rheological properties of the paste. • The absorption capacity of silica gel mainly governed the rheological properties of the paste. • The absorption capacity of silica gel was dependent on its pore structure and surface properties. • Monoethanolamine mitigates the negative effect of carbonated recycled cement paste powder on the paste'rheology. [ABSTRACT FROM AUTHOR]

Several attempts have been made to achieve considerable energy savings in concrete buildings by using phase change materials (PCMs). However, PCM leakage can affect both the PCMs' efficiency and the overall properties of concrete which consequently limit their application in buildings. To overcome this issue, this study proposes to develop a novel core-shell structured phase change material aggregates (AGGs PCM) to capture and store solar energy in the building envelope for space heating and cooling applications. The thermophysical properties of AGGs PCM and the thermal performance of AGGs PCM in concrete panels under the actual climate conditions of southern China were tested. The obtained results demonstrate significant PCM leakage prevention and enhancement of the thermal performances of the concrete panel. The AGGs PCM -concrete panel was able to reduce the peak temperature by 1 °C, indicating improved thermal comfort and electricity saving potential. Better performances could be achieved by increasing the mPCMs content into AGGs PCM or by selecting a PCM with a more suitable phase transition temperature to allow a more efficient heat storage and release process. Image 1 • MPCM was successfully incorporated during the granulation process of artificial aggregates. • Coating PCM-aggregates with epoxy could prevent further PCM leakage under harsh environments. • Aggregates with high mPCM content exhibited good latent heat and low crushing strength. • Peak temperature of PCM-concrete panels decreased by about 1 °C which provides an energy saving of 3%. • PCM-aggregates could be used in buildings envelopes for space cooling/heating management. [ABSTRACT FROM AUTHOR]

The use of carbonated recycled cement paste powder (RCPP) as a mineral admixture affects the properties of the cement paste through multiple effects. This study proposes a model to decouple and quantify these effects based on their contribution to the compactness (1 − porosity) of the paste. Experimental results showed that the filler effect significantly contributed to the increase in compactness by 10.4 %–55.9 % at 1d-28d, while the contribution of the pozzolanic effect of silica gel was 2.7 %–7.3 % at 1d and then reduced remarkably at 3d. The nucleation effect contributed to the compactness of paste by 7.0 %–12.8 % within 3d. The contribution of the chemical effect varied largely among the different pastes at 1d and 28d. This explains the difference observed in the properties of the pastes. Increasing the carbonation time and temperature during wet carbonation of RCPP could improve the properties of paste by increasing the total contribution of chemical, nucleation, and pozzolanic effects. [ABSTRACT FROM AUTHOR]

Due to the population growth and the increased reliance on cooling and heating systems, buildings have become the largest energy consumer worldwide. The use of phase change material (PCM) has shown great potential to reduce the annual cooling and heating load by up to 50%. Nowadays, the direct incorporation of PCM in cement-based materials (CBM) is creating a considerable debate in the research community with regards to the proper selection and the beneficial utilization of PCM (microencapsulated or composite) in CBM. Therefore, this paper reviews the pros and cons of using microencapsulated and composite PCM in CBM by highlighting the mechanisms involved in the mechanical strength loss and thermal properties enhancement. Generally, a high thermal energy storage CBM was obtained. However, PCM exhibited a negative effect on the compressive strength of CBM. In view of the literature review, the compressive strength reduction varies considerably with no clear trend which is understandable in view of the differences in mix designs as well as the variety of materials used in each study. Finally, an up-to-date PCM case studies, gaps and future directions are also presented to provide a reliable basis and helpful reference for the future development of eco-friendly and energy-efficient building materials containing PCM. • Pros and cons of using mPCM and cPCM in CBM are reviewed and compared. • Both mPCM and cPCM has generally similar impacts on the CBM performances. • Factors affecting the strength loss of CBM by PCM are discussed in detail. • Encapsulation doesn't seem to be a promising solution to prevent CBM's strength loss. • Case studies, current research gaps and future directions are presented. [ABSTRACT FROM AUTHOR]

Abstract Paraffin as a phase change material showed a great potential to promote energy efficiency in buildings due to its unique thermo-physical properties. However, its low thermal conductivity can negatively impact the charging-discharging process and affect the heat transfer efficiency. Previously, many researchers have focused on using shape-stabilized materials and additives to form paraffinic phase change materials (PPCM) with a high thermal conductivity. However, these techniques resulted in the reduction of the total amount of paraffin incorporated into the PPCM and thus lowered the overall thermal efficiency. Based on the analyzed literature data, this paper suggests that the paraffin content in the PPCM should be equal or higher than 50.0% to achieve better performances. Therefore, exploring novel composites and additives to form thermally stable and efficient PPCM with enhanced heat transfer could be a topic of interest to encourage and implement more sustainable practices in the building industry. [ABSTRACT FROM AUTHOR]

In the present work, the synergetic effect of fly ash (FA) and ground granulated blast furnace slag (GGBS) on the early compressive strength and microstructure development of CO 2 -cured mortars was investigated. A rim of several micrometers was found around carbonated cement particles, which contained not only silica-rich gel but also crystal calcium carbonate. The calcium carbonate formed around the cement particles were surrounded by an amorphous layer of around 3 nm, while no layers were observed around the calcite formed on FA or GGBS particles. The calcite formed on FA particles were hexagonal plate shaped, while the one on GGBS particles were rhombohedral shaped. The use of FA resulted in the increase of crystal size and crystallinity of calcite, while GGBS decreased the crystal size of calcite. The incorporation of FA and GGBS increased the calcite content and polymerization of silica-rich gel. However, this didn't result in a higher compressive strength. This was due to the looser microstructure and nanopores within the carbonation products compared to the pure ordinary Portland cement sample. The compressive strength of the ternary binder system showed linear relationship with capillary pores and the crystal size of calcite. Moreover, the effect of GGBS on the compressive strength reduction was more obvious than that of FA. [ABSTRACT FROM AUTHOR]

This study investigated the effect of temperature (5 °C–50 °C) on the carbonation process, compressive strength and microstructure of CO 2 -cured cement paste. Results showed that the carbonation process and rate were significantly affected by temperature and time. When the curing temperature increased, the rate of improvement of cement paste's properties was accelerated. The carbonation reaction was mainly kinetically controlled by product layer diffusion with an activation energy of about 10.8 kJ/mol. Temperature had greatly affected the structural transformation, morphological changes, size and amounts of calcium carbonate polymorphs (calcite, aragonite and vaterite) as well as their degree of crystallinity and decomposition temperature. Alongside calcite, vaterite and aragonite were formed at low and high curing temperatures, respectively. Apart from microstructure, the compressive strength was also found to be very sensitive to temperature and carbonation products. The relationship between the amount of different carbonate polymorphs and the compressive strength was also provided. [ABSTRACT FROM AUTHOR]

The phase change materials are considered an attractive way to reduce energy consumption thanks to their heat storage capacity. Their incorporation in the construction materials allows the energy to be an integral part of the building structure. Even though PCMs have shown their reliability from a thermal point of view, some drawbacks linked to their use were emphasized such as the loss of the compressive strength of the PCM-material. This paper attempts to provide an explanation by the investigation of the hydration kinetic of PCM-mortars. The semi-adiabatic Langavant test was adapted to this case. The numerical diffuse element method was used for the computation of the heat flux, which is a compulsory step for the determination of the hydration degree. The results showed a lower heat released by the PCM mortars compared to a control mortar as well as a delay in the hydration progress with the addition of PCMs. [ABSTRACT FROM AUTHOR]

This study aims to elucidate the effect of different mixing speeds on microencapsulated phase change material (mPCM) and examine the associated degradation mechanism of compressive strength of cement-paste. Experimental results showed that moderate to high mixing speed led to the damage of mPCM particles and consequently the PCM leakage. The PCM leakage was evidenced by changes in the rheological properties of the mPCM-pastes. The early age compressive strength seemed to be more sensitive to the PCM leakage than the 28-day compressive strength. The XRD results showed no evidence of any chemical change in the mPCM-paste associated with this leakage. Therefore, the lowered compressive strength in mPCM-paste was mainly ascribed to the decrease in the heat of hydration along with a significant increase in porosity and coarsening of pore structure. [ABSTRACT FROM AUTHOR]

• Simplex design method was used to elucidate the composition-dependent mechanism. • Composition changes and properties were correlated via graphical visualization. • Relationships between the paste composition and its properties were developed. This paper aims to elucidate the effect of changes in the mix composition on the properties of Portland cement (PC)-metakaolin (MK)-limestone (LS) ternary system. To achieve this, the mixture proportion was optimized using the simplex design method and its effect on the properties of the binder was evaluated experimentally and correlated via graphical visualization. Experimental results confirmed the enhancement and acceleration of kinetics of cement hydration by LS and MK. However, a higher porosity was noticed at early age and was attributed to the high reactivity of MK which hindered it from acting as an effective filler. Therefore, the correlation between the optimum mix design and compressive strength was found to be dependent on the paste age. The findings of this paper would contribute to a better understanding of the dependence of the properties of PC-MK-LS ternary system on its composition. [ABSTRACT FROM AUTHOR]

• PCM aggregates with a core-shell structure were produced through a two-step pelletization process. • CO 2 curing enhanced the aggregates' strength. • The PCM leakage from the aggregates was analysed. • Leak free PCM aggregates with a good latent heat capacity (∼18 kJ/kg) were obtained. This study aims to develop leak-free phase change material (PCM)-aggregates through a two-step pelletization process. Microencapsulated PCM (mPCM) was incorporated into the core of the aggregate during the granulation process and then coated with a PCM-free shell to overcome the PCM leakage. The thermal properties of pellets cured under CO 2 and natural air, including their enthalpy and thermal conductivity as well as their thermal stability were measured and compared using differential scanning calorimeter, thermogravimetric analyses and transient plane source method. The effect of both mPCM content and CO 2 curing on the strength of the aggregates was also analyzed. The results revealed that mPCM can be used to produce lightweight aggregates with a distinct core-shell structure having an oven-dry bulk density, water absorption and latent heat of about 788 kg/m3, 14% and 18 kJ/kg, respectively. In addition, the shell layer can effectively prevent the leakage of the PCM and can be further densified by CO 2 curing. In addition, CO 2 curing contributed to the improvement of the overall physical properties and early strength development of the aggregates. The developed leak-free PCM-aggregates would then allow adding PCM into the concrete mix as an inert material and hence suppress the degradation of mechanical strength and high-water demand caused by the direct use of mPCM in concrete. [ABSTRACT FROM AUTHOR]

Wet carbonation is deemed a successful approach to recycling waste concrete powder. Controlling the growth and properties of products in the recycled cement paste powder (CPP) is highly dependent on the wet carbonation conditions. Therefore, this study aims to examine the effect of wet carbonation parameters on wet carbonation products in CPP. The wet carbonation of CPP resulted in mixed distribution of silica gel and CaCO 3 without significant layering on the CaCO 3. In contrast, silica gel covered the outside of the CaCO 3 in the case of dry carbonation. Increasing the temperature from 25 °C to 80 °C promoted and accelerated the crystallization and growth of amorphous CaCO 3 , increased the crystallite size of CaCO 3 by 1.1–5.1 nm, and favored the formation of aragonite and vaterite; however, it also led to a significant crystal defect and/or distortion within CaCO 3. Higher temperatures also promoted silica gel formation and increased its polymerization degree by 68.2%. On the other hand, increasing the CO 2 flow rate from 3 L/min to 5 L/min facilitated the crystallization and growth of CaCO 3 and contributed to the increase in the crystallite size of CaCO 3 by 3.0–6.6 nm. Higher CO 2 flow led to the incorporation of aluminum into silica gel and resulted in the transformation of its gel pores into capillary pores. The findings of this study contribute to a better understanding of the best experimental parameters to achieve a more efficient and effective concrete waste recycling process. • Carbonation of CPP in an aqueous solution was performed under various conditions. • Higher CO 2 flow rate had a negligible effect on CaCO 3 polymorphs. • Higher temperature and CO 2 flow rate promoted the crystallization and growth of CaCO 3. • Elevated temperature enhanced silica gel formation and its polymerization. • CO 2 flow rate influenced the pore structure and aluminum uptake in silica gel. [ABSTRACT FROM AUTHOR]

Internal curing by superabsorbent polymer (SAP) is an effective method to mitigate the autogenous shrinkage of cement‐based materials with low water‐to‐cement ratio (w/c). In this study, the water absorption/desorption kinetics of SAP were studied quantitatively in blended cement pastes with ultra‐low w/c. An absorption process at a rate of 0 to 6 g/(g h) was calculated at early ages. After that, SAPs showed mainly two distinct water desorption behaviors with a rate of 0 to 1.1 g/(g h), which was mainly governed by the osmotic pressure and capillary pressure triggered by the drop of internal relative humidity (IRH). The size and amount of SAP played a predominant role in controlling its absorption and desorption kinetics in the cement paste. Compared with ordinary Portland cement, a different desorption process with a higher release rate was noticed in binary and ternary cement pastes, primarily due to the changes in osmotic pressure resulting from the acceleration of cement hydration by silica fume at early ages. Overall, the mitigation of autogenous shrinkage is found to be highly dependent on SAP's absorption and desorption kinetics. [ABSTRACT FROM AUTHOR]