Search

Improving the very early age strength of precast concrete components at ambient temperature and ensuring the development of later strength is of significant engineering importance. This objective was successfully achieved by incorporating a specific percentage of 0–3% CSH seeds (CSHs) and 5%-20% calcium sulphoaluminate cement (CSA) into Portland cement (PC). The hydration, strength and microstructure evolution of Portland cement-calcium sulphoaluminate cement-CSH seeds cementitious system were investigated. Hydration heat tests reveal that CSHs effectively accelerated the early hydration of the slurry within the first 12 h without affecting its later hydration. CSHs and CSA acted synergistically to enhance hydration kinetics. However, it is crucial to control the proportion of CSA within the range of 5%-10%; exceeding this ratio can severely inhibit the hydration of silicates. Strength tests indicate that the addition of CSHs and CSA can increase the compressive and flexural strengths of mortar within the first 12 h by 282% and 208%, respectively, without impacting the development of its later-age strength. Together, they synergistically provide favorable support for the strength and toughness of matrix. Based on linear regression analysis and nitrogen adsorption and desorption tests, it was concluded that CSHs enhance the hydration dependence of matrix strength, while CSA diminishes this characteristic. This is because CSHs refine the pore size distribution of the paste, increasing the proportion of micropores, whereas CSA promotes the formation of more mesopores and macropores, leading to coarser pores; however, 5% CSA is beneficial for further refining the pore structure. The microcosmic phase evolution of the early-strength cementitious system was analyzed through X-ray diffraction and scanning electron microscope-energy dispersive spectrometer experiments. Results demonstrate that low proportions of CSA and CSHs promote the co-growth of ettringite and C-S-H gel, ensuring a more rapid formation of a dense hydration network in the early stages, thereby accelerating strength development. These findings provide a reference for the design and preparation of precast concrete. • CSHs and CSA synergistically enhance the hydration and strength development of cement matrix at an early stage. • The early-strength cementitious system can achieve a strength of 10 MPa at 6 h and 70 MPa at 28 d using 2 % CSHs and 10 % CSA. • Appropriate amounts of CSHs and CSA promote the rapid formation and stable growth of a dense microstructure. • CSHs enhance the hydration dependency of matrix strength, while CSA reduces it. • PC-CSA-CSHs is an efficient, benign and green ultra-early strength cementitious system. [ABSTRACT FROM AUTHOR]

In order to improve the crack resistance toughness and investigate the capillary water absorption (sorptivity) characteristics of ceramsite lightweight concrete (CLWC), the current study has examined the performance characteristics of locally accessible polypropylene (PP) fiber and rubber-reinforced lightweight concrete. An investigation on CLWC's strength, ductility, and sorptivity was addressed in this research. This study examined how fiber and rubber affect CLWC characteristics. Thus, the experiment maintained concrete mix design and fiber and rubber properties while varying fiber and rubber dosages from 0.05% to 0.15% and 0.5–1.5%. Multiple tests on CLWC specimens showed promising compressive, flexural, and toughness results. In the sorptivity test, fibers inhibit CLWC water absorption, assessing lightweight concrete porosity and permeability. SEM examined the ceramsite, rubber, fiber, and mortar interaction microstructure. Notably, strength capacity significantly improved compared to conventional lightweight concrete. Beam flexure testing indicated a maximum 62.79% toughness enhancement. Additionally, the first-crack load increased by 31.83%, and the ultimate load increased by 32.34% over control beams. The macro crack strength of interconnecting structures is improved by fiber and rubber. Several energy dissipation pathways gave ceramsite lightweight materials enhanced flexural toughness. • This study examined the strength, ductility, and durability of Fiber Reinforced Ceramsite Lightweight Concrete. • To investigate the impact of fiber and rubber content on Ceramsite Lightweight Concrete (CLWC) characteristics. • Compressive, flexural, and toughness improvement and capacity increase were observed. • CLWC has demonstrated enhanced durability compared to conventional lightweight concrete. [ABSTRACT FROM AUTHOR]

The steam curing technology is worldwide applied in the production of concrete prefabricated components, including the production of track slab and girder used for the high‐speed railway in China. However, the steam curing process at elevated temperature will often generate the heat damage on concrete and thus degrade the long‐term performance of the steam‐cured concrete prefabricated components. It is very important to deeply understand the mechanism of heat damage and thus to find effective method reducing or avoiding the damage of steam curing on concrete. The main purpose of this paper is to systematically classify the types of thermal damages on concrete during the steam curing and its mechanism. The influences of main factors on three thermal damages such as the unrecoverable expansion deformation, the surface layer defect, and the embrittlement of the steam‐cured concrete are discussed in detail. The controlling methods of thermal damages including optimization of the steam curing regime and mixing proportions, the addition of supplementary additives, the self‐healing technology, and other curing technology are compared and summarized based on the literatures. Finally, suggestions for future research are proposed in order to effectively reduce or even avoid the thermal damage of the steam‐cured concrete. And also, some new technology for developing the green and high performance early strength concrete with low CO2 emission are presented. [ABSTRACT FROM AUTHOR]

In this paper, calcium silicate hydrate (CSH) gel and calcium silicate hydrate doped with asphalt emulsion (EACSH) were synthesised using Na2SiO3•9H2O, Ca (NO3)2•4H2O, NaOH, deionised water and anionic asphalt emulsion. N2 isothermal adsorption, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the effect of asphalt emulsion on morphology and porosity of CSH. The Frenkel–Halsey–Hill (FHH) model was used to analyse the surface fractal characteristics. The results showed that the asphalt emulsion had little effects on the change of specific surface areas and the distribution of the micropores for CSH gel, which may be related to the absence of the intercalation reaction and the "opening" effect. The asphalt emulsion could promote the formation of mesoporous hydrated calcium silicate and decreased the number of mesopores in CSH gel but had little effects on the macroporous and microporous structure of CSH. The calculation results of the FHH model showed that the fractal characteristics between CSH and EACSH were different. The emulsifier may adsorb CSH gels result in globular accumulation state. [ABSTRACT FROM AUTHOR]

To investigate the reasons for the mitigation of drying shrinkage but earlier cracking in limestone powder cement paste, various admixtures such as fly ash, metakaolin, super-absorbent polymer, and expansion agent were selected for the above-mentioned experiments. The effects of mixing two admixtures on the drying shrinkage deformation and crack resistance performance of the limestone powder-cement paste was studied. Additionally, hydration exotherm, hydration products, microscopic morphology of samples were analyzed to understand the underlying mechanisms. Based on the hydration process, the addition of fly ash and metakaolin can promote the formation of carbon aluminate in the reaction system, thereby reducing the porosity. Fly ash is more beneficial for the hydration heat peak value of cement paste, effectively eliminating temperature strain. The results indicate that effects of mixing two admixtures on the improvement of drying shrinkage and crack resistance of limestone powder cement paste are much better than using a single admixture. Among them, the combination of metakaolin and expansion agent shows the best overall mitigating effect on the drying shrinkage and crack resistance of limestone powder cement paste. This compound admixtures reduces the drying shrinkage of the paste by approximately 30% and delays the cracking time of the specimens by 34.4 h. • The utilization of limestone powder in limestone powder cement paste can be effectively enhanced by mixing two admixtures. • Using a smaller ring size for the ring test to monitor the cracking resistance of cement paste. • The application of linear fitting revealed that the moisture loss characteristics of cement paste manifest in two stages. • Analyzing the reasons for the mitigation of drying shrinkage but earlier cracking in limestone powder cement paste. [ABSTRACT FROM AUTHOR]

• C-S-H seeds and sulphoaluminate cement were used to prepared RH-UHPC. • The flexural load–deflection response of RH-UHPC was studied by AE technology. • The flexural failure pattern, strength, energy absorption capacity, and toughness index of RH-UHPC were investigated. • Micromorphology, phase composition, and pore structure of RH-UHPC were studied. With the increasing requirements for emergency repair projects, there is a pressing need for high-quality repair materials. In this work, a series of rapid hardening ultra-high performance concrete (RH-UHPC) were prepared by using C-S-H seeds and SAC as early-strength agents. The effects of these early-strength agents on RH-UHPC's flexural behaviors, including failure pattern, strength, energy absorption capacity, and toughness index, were investigated. Also, the variations of acoustic emission signals and microstructure were studied to provide a thorough insight into the influence of early-strength agents on RH-UHPC. The results show that C-S-H seeds and SAC exhibited a good effect on improving the 1-day flexural strength of RH-UHPC, but increased the risk of shear failure at 28 days. The flexural strength, energy absorption capacity, and toughness of RH-UHPC at 28 days were reduced by adding C-S-H seeds. However, combining C-S-H seeds with SAC alleviated this reduction. Moreover, incorporating early-strength agents enhanced the ringing counts, AE energy, damage rate, and the proportion of shear cracks. The noticeable increase in r value (i.e., RA/AF) judged the damage stage of RH-UHPC more reliably. Micro-analysis revealed that introducing C-S-H seeds increased the internal cracks and the Ca/Si ratio of C-S-H gel, but the hybrid of C-S-H seeds and SAC partially mitigated above problem. The incorporation of SAC notably increased the AFt content and decreased the CH content. C-S-H seeds presented little effect on the hydration degree of RH-UHPC, but roughened the pore size and enlarged the average pore size. [ABSTRACT FROM AUTHOR]

Steam curing is a crucial stage for the strength development of steam-cured concrete. This study comprehensively investigated the hydration kinetics, mechanical properties, and autogenous shrinkage (AS) of cement pastes during steam curing. A hydration-dependent analytical method was proposed to analyze the mechanisms governing the development of mechanical properties and AS of steam-cured cement pastes (SCPs). Results revealed that in this investigated curing regimes, the peak hydration rate of SCPs was approximately 7 times higher than that of standard-cured pastes (NCPs). SCPs exhibited faster time-dependent mechanical property development but slower hydration-dependent mechanical property development than NCPs. This difference was primarily attributed to variations in initial structure establishment and free water content. Moreover, an elevated curing temperature reduced the growth rate of hydration-dependent AS due to large capillary pores and low surface tension, which suggested that AS should not be considered as a cause of heat damage to SCPs. [ABSTRACT FROM AUTHOR]

Electrolytic manganese residue (EMR) stockpiles contain significant amounts of Mn2+ and NH 4 +-N which pose a risk of environmental pollution. For EMR safe disposal, an innovative approach is proposed that involves direct sodium silicate-sodium hydroxide (Na 2 SiO 3 –NaOH) collaborative technology. This approach utilises Na 2 SiO 3 and NaOH as the solidifying agent and activator, respectively, to treat EMR without hazardous effects. The study also provides insights into the kinetics of Mn2+ leaching under the effect of Na 2 SiO 3 –NaOH. Leaching efficiency was determined by varying parameters such as stirring rate, reaction temperature, pH of the initial solution, Na 2 SiO 3 concentration, and reaction time to investigate the efficacy of this method. The study indicates that the co-treatment technology of Na 2 SiO 3 –NaOH can achieve maximum solidification efficiencies of 99.7% and 98.2% for Mn2+ and NH 4 +-N, respectively. The process can successfully solidify Mn2+ by synthesising Mn(OH) 2 and MnSiO 3 in an alkaline environment under optimal conditions including stirring rate of 450 rpm, initial solution pH of 8, test temperature of 40 °C, test time of 420 min, and Na 2 SiO 3 content of 5%. The findings of this study have confirmed that surface chemistry plays a vital role in regulating the test rate and the proposed equation accurately describes Mn2+ leaching kinetics. Overall, the co-treatment technology involving Na 2 SiO 3 –NaOH is a viable solution for EMR resource utilisation without compromising environmental safety. This method has the potential to be implemented for other waste streams with comparable compositions, ultimately promoting the sustainable management of waste. [Display omitted] • A direct Na 2 SiO 3 –NaOH collaborative treatment technology for Mn residue. • Synergistic impact greatly enhances the Mn2+ leaching efficiency. • Treatment procedure is well described by Mn2+ kinetic equation. • The maximum solidification efficiency of NH 4 +-N and Mn2+ are 98.2% and 99.7%. • The ideal strength of Mn residue-based paste has the potential as binder material. [ABSTRACT FROM AUTHOR]

• The influence and mechanism of low temperature (180℃) calcined electrolytic manganese residue (EMR) on the early-age hydration of cement paste were studied. • The incorporation of calcined EMR leads to a higher Ca concentration and a lower pH value in the pore solution, resulting in a later depletion of gyspsum and decrease of portlandite and C-S-H formed. • The hemihydrate gypsum in EMR calcined at 180℃ provides a key dissolution-inhibiting mechanism during the 6 h-12 h phase, thus inhibiting the hydration of C 3 S and C 3 A at this period. • The incorporation of calcined EMR significantly lowers contents of hydration products during the 6 h-12 h phase, thus hindering the strength development of cement pastes. Low temperature calcination is an appropriate method to pretreat the electrolytic manganese residue (EMR). 180℃ is selected as an optimal temperature to apply to the present study, since the hemihydrate gypsum formed at 180℃ can improve the reactivity of EMR at no expense of considerable energy consumption and environmental pollution. This study examines how 180 °C-calcined EMR affects the composition of the pore solution and solid phases of cement paste as well as the hydration kinetics at early ages. The results indicate that the inhibition of EMR on the early-age hydration of cement paste mainly results from the dissolution behavior of hemihydrate gypsum in 180℃-calcined EMR during the 6 h-12 h period. A large-scale dissolution of hemihydrate gypsum after 6 h, released from EMR, leads to an increased Ca and S concentrations at the expense of a postponed consumption of gypsum, thus a reduced C 3 A reaction and a lower ettringite formation rate. In addition, the adding EMR significantly decreases the degree of pore solution in supersaturated state concerning portlandite (CH) and calcium silicate hydrate (C-S-H) gel during the 6 h-12 h period, thus hindering the early formation of hydration products by an inhibited C 3 S reaction. Moreover, the inhibition mechanism of 180℃-calcined EMR during the 6 h-12 h period is further emphasized on the early-age hydration. [ABSTRACT FROM AUTHOR]

• The drying shrinkage behavior of mortars under low vacuum conditions was studied. • The low vacuum increased mass loss and drying shrinkage. • The mechanisms of shrinkage under low vacuum conditions were analyzed. • Incorporation of FA and SRA reduced the drying shrinkage under low vacuum conditions. In this work, the time-dependent drying shrinkage behaviors of cement mortar under low vacuum and standard drying conditions were tested and compared, in which the specimens were prepared based on various mixtures. Also, a series of microscopic tests were conducted to investigate the hydration and microstructure of the prepared specimens, and thus, to explain the drying shrinkage behavior of different specimens. The results showed that compared with standard drying condition, the specimens under the low vacuum condition exhibited higher drying shrinkage and mass loss, but lower sensitivity of drying shrinkage to mass loss. Under both conditions, the incorporation of fly ash and silica fume or shrinkage-reducing agent could greatly decrease the drying shrinkage, with the better performance identified in the case of fly ash and shrinkage-reducing agent; while the addition of sulphoaluminate cement had no inhibiting effect on the drying shrinkage deformation. Although the specimen solely based on sulphoaluminate cement showed the lowest drying shrinkage under standard drying condition, it exhibited greater drying shrinkage than the Portland cement specimens under low vacuum conditions. The microscopic test results suggested that low vacuum treatment could decrease the hydration degree while the decomposition of ettringite in the sulphoaluminate cement could be observed under low vacuum conditions. Besides, the gel pore volume fractions decreased while the cumulative total pore volume increased after low vacuum treatment, which resulted in a loose and porous microstructure with high vulnerability to drying shrinkage. [ABSTRACT FROM AUTHOR]

In this research, the electrolytic manganese residue (EMR) based belite-ye'elimite-ferrite (E-BYF) clinker composed of 51.6 % belite, 25.6 % iron phase, 15.8 % ye'elimite and 6.5 % over-burned anhydrite phase was manufactured successfully at 1200 °C _ 30 min by utilizing EMR (45.5 %) and additional CaO and Al 2 O 3. The existence of iron-rich and heavy metal phases was a potential driving force for achieving near complete calcination at 1200 °C _30 min. The iron ions (8.4 %) and the over-burned anhydrite phase partially replaced the Al3+ ions by entering the ye'elimite lattice and provided enough SO 3 (5.9 %) to help stabilize ye'elimite and β-C 2 S formation, respectively. Layered double hydroxides such as AFm phase and strätlingite formed dense microstructure and improved pastes strength as a new rigid skeleton. The formation of rigid solid skeleton-flexible gel embedded co-support system provided a reliable solution for eliminating inherent strength plateau (3-day of 45.9 MPa and 60-day of 107.0 MPa). In this system, the solid-phase hydrates as the main skeleton offered sufficient rigid-supporting, while the gels hydrates as the auxiliary fluid that filled into the pores of the formed skeleton gave the adequately flexible-supporting. In addition, the pastes showed an excellent stabilization ability of heavy metals. The E-BYF system has great potential in reducing CO 2 emissions (0.58 kg/kg and 1.36 kg·/MPa·m3) and cost. This work provides a new perspective for a high-quality solution to the strength plateau while achieving a high value-added utilization of EMR. [ABSTRACT FROM AUTHOR]

• The physical effect of intense UV radiation accelerates the mass loss of the cement mortar. • The chemical effect of the intense UV radiation exacerbates the carbonation of the cement mortar. • FA and GGBS have the effect of reducing drying shrinkage under conditions of intense UV radiation. • The incorporation of FA and GGBS weakens the carbonation resistance of the cement mortar. The intense UV irradiation factor in the plateau area is easy to ignore, but it may have adverse effects on the microstructure and properties of concrete. Theredore, to clarify the evolution characteristics and the corresponding mechanism of the drying shrinkage of cement-based materials under intense UV irradiation environments at high altitudes cement mortars incorporating three types of mineral admixture were prepared to investigate the drying shrinkage, mass loss and microstructure, respectively. The hydration process and microstructure of samples were discussed in detail by microscopic experiments including TG-DTG, MIP, XRD, and IR patterns analysis. The results show that the mass loss and drying shrinkage of the cement-mineral admixture mortar exposed to intense UV irradiation were higher than those under the standard environment. Under intense UV radiation environment, the total porosity, mesoporosity (<50 nm), and carbonization degree of each group of samples increased. However, UV irradiation did not change the phase composition, chemical bond type, and polymerization degree of the C S H gel of the cement-based material. The incorporation of fly ash and slag resulted in the reduction of drying shrinkage of mortars, an increase in carbonation degree, and decreasing the hydration degree. [ABSTRACT FROM AUTHOR]

The direct stockpiling of electrolytic manganese residues (EMR) poses a major environmental issue, and more eco-friendly disposal is urgently needed. The combination of cement solidified waste (CSW) and direct electric curing (DEC) provides a potential solution for hazard-free value-added utilization of EMR. The effects of DEC voltages and EMR dosages on mechanical properties, hydrated products, pore structure of mixture were investigated. The influencing mechanism of DEC on the properties of cement hydration was explored in-depth using TG and XRD results. The environmental and economic evolution of DEC was analyzed, and the leaching test was conducted to evaluate the immobilization of heavy metals. Results indicate that cement-EMR pastes cured in higher DEC voltage and reduced EMR dosage increase mechanical strength and improve pore structure and capillary water absorption with respect to indoor curing (IC). The increased cement dosage improves the effectiveness of CSW, while the increased DEC voltage enhances the ionic driving force. The boosted ettringite formation occurs in system after introducing DEC and amplifying the DEC voltage. The improvement of ion concentration in DEC accelerates the formation of hydration products. The CO 2 -e per MPa (EIF) and cost per MPa (CIF) values of paste DMP-7 cured in 12V-DEC exhibit the lowest values with respect to those cured in other voltages and IC. The decrease in the leaching amount of Mn2+ and NH 4 +-N as the DEC voltage increases, and the 28-d leaching concentration of Mn2+ and NH 4 +-N in pastes are in accordance with the national standards. The application of DEC and cement-solidified disposal for EMR could provide a potential solution for high-value and large-capacity disposal of hazardous solid waste. [Display omitted] • Combined with cement hydration and DEC realizes high dose hazard-free value-added utilization of EMR. • DEC promotes cement hydration for high-early strength and EMR solidification with respect to IC. • The improvement in strength of paste cured in DEC is boosted by ionic migration and pore structure. • Mn2+ and NH 4 +-N below national standards at high-alkali condition from cement hydration. [ABSTRACT FROM AUTHOR]

The global cement industry is facing severe pressure to reduce emissions, it is of great importance for developing low-carbon cement-based materials. Natural hydraulic lime (NHL), as an environmentally friendly binder, can be used to prepare green concrete instead of cement. In this paper, a thermodynamic simulation method was employed to analyze the hydration products of the NHL-mineral admixture system. The strength of mortars with NHL-mineral admixtures was tested. The environmental impacts of different NHL-mineral admixtures were analyzed based on the embodied CO 2 (EC) indicators. The relationships between the main hydration product (CSH gel) in the NHL-mineral admixture system, the mechanical strength, and EC were established. In addition, considering the best mechanical properties and low carbon emissions, the optimal composition of the system was discussed. The results showed that in the NHL-mineral admixture system, different composition ratios of mineral admixture and NHL had significant effects on CSH gel content and EC. The optimal compositions of binary and ternary systems of different NHL-mineral admixtures were analyzed. Among them, the NHL-GGBS-SF ternary system is the best, in which the CSH gel content is greater than 80%, and the EC is only one-third of Portland cement and one-half of pure NHL systems, respectively. This achievement will provide important technical support for the development of sustainable cement-based materials. [ABSTRACT FROM AUTHOR]

• Higher calcination temperature reduced the dissolved degree of Al in sludge ash. • S600 ash promoted the formation of Al-bearing products but inhibited the C 3 S hydration significantly. • The reaction of S800 ash with cement contributed to more hydration heat and hydration products. Sewage sludge ash has potential to be used as supplementary cementitious material in the production of building materials. The chemical effect of sewage sludge ash on early-age hydration of cement was investigated in this study. Two types of sludge ash calcined at 600 °C (S600) and 800 °C (S800) were blended with cement for analysis of hydration heat evolution, solid phase assemblage and aqueous composition. The aluminate dissolution of S600 ash promoted the formation of ettringite and consumption of gypsum, resulting in a high initial hydration heat. However, high concentrations of Al and Si caused by continuous dissolution of aluminate and silicate in S600 ash inhibited significantly the C 3 S dissolution. Interestingly, S800 ash had slight effect on early cement hydration since higher calcination temperature decreased the activity of aluminate. As compared with the reference, cumulative hydration heat of blended paste with 30% S800 ash at 7 days was increased by 18.72% indicating the occurrence of reaction between sludge ash and cement. Further study is recommended to focus on the long-term performance of cement-based materials blended with sludge ash. [ABSTRACT FROM AUTHOR]

Degradation in grade of manganese ore aggravates the complexity of electrolytic manganese residue (EMR). Calcination is one of the most practical pretreatment methods to improve EMR activity and dispose the hazardous elements. In this paper, the evolution of mineral phase, pozzolanic activity, pore structure and harmful components induced by calcining EMR was investigated. The results show that EMR calcined at 800 °C has the strength activity index (SAI) of 84.79 at 28 d, which is attributed to the decomposition of dihydrate gypsum and the formation of activated calcium, silicon and aluminum oxide. The formation of β-type hemihydrate gypsum increases the pozzolan activity, while the latter is limited by the formation of stable Mn-spinel (Mn 3 O 4) and Mn-hercynite (MnFe 2 O 4). In the EMR-doped mortar matrix, the production of a large amount of ettringite due to the existence of gypsum, as well as common C-S-H, portlandite and AFm, which strongly verify the pozzolanic activity of EMR. Leaching results show that Mn2+ and NH 4 +-N could not be eliminated completely at low temperature (<600 °C) , but could be completely stabilized in the alkaline environment provided by the cement. The Mn2+ and NH 4 +-N levels in mortar are fully below the regulatory standards when calcinated above 800 °C. All heavy metals are fixed in the cement and calcination process, ensuring the cleaner utilization of EMR in building materials. [Display omitted] • EMR calcined at 800 °C has the optimum strength activity index of 84.79 at 28-d. • Pozzolan activity of EMR is boosted in β-CaSO 4 ·0.5H 2 O and weakened in Mn 3 O 4 and MnFe 2 O 4. • Presence of gypsum in EMR retards the cement hydration and forms ettringite. • Mn2+ and NH 4 +-N below national standards at calcination above 800 °C. [ABSTRACT FROM AUTHOR]

• Physicochemical properties and pozzolanic activity of sludge ashes were investigated. • The sludge ash calcined at 800 ℃ presented high pozzolanic activity. • Sludge ash addition enhanced the formation of Al-bearing hydrates. • No leaching risk was detected for the use of sludge ash in building material. The application of aluminum-based flocculant in wastewater treatment results in a large amount of aluminum-rich sewage sludge. This work investigated the influence of calcination process on physicochemical characteristics and pozzolanic activity of aluminum (Al)-rich sludge ash and studied the effect of sludge ash on cement hydration. The results showed that higher calcination temperature from 600 ℃ to 900 ℃ increased the amorphous content in sludge ash. The pozzolanic activity of sludge ash calcined at 800 ℃ and 900 ℃ was confirmed by Frattini test. In view of strength activity index of blended mortar and energy conservation, the optimal calcination condition of sewage sludge ash was calcined at 800 ℃ with air-cooling. The addition of sludge ash promoted the transformation of ettringite to monosulfate phase in cement paste. However, the high Al concentration dissolved from S6 and S7 ash inhibited significantly the cement hydration and resulted in low compressive strength values of the blended mortars. The pozzolanic reaction of S8 and S9 ash produced more hydration heat and additional Al-bearing products such as katoite and monosulfate which contributed to the strength development of mortars. Furthermore, the heavy metals in sewage sludge can be immobilized in ash structure during calcination process and the structure of hydration products, which ensures the environmental security of sludge ash utilization in construction materials. [ABSTRACT FROM AUTHOR]