Blended Cement Research Articles

Low clinker systems - Towards a rational use of SCMs for optimal performance

Progress in understanding the use of SCMs in blended Portland cement and related effects is reviewed. An optimized use of cement components will avoid wasting unreacted particles that do not contribute to the mechanical and durability performances. The reactivity of cement components increases with fineness and by controlled production processes. Clinker may become a minor component in the cementitious mix due to the optimized particle packing of blended cements. An optimized mineralogy of the clinker coupled to the addition of activators can help to further reduce its use in composite cements while maintaining concrete performance. Other cement constituents introduce different filler and chemical effects to the overall reaction and contributes differently to the performance. Filler and chemical effects influence the hydrates assemblage and in particular C-S-H formation, morphology, and chemical composition. The cement and concrete properties at different ages are tightly linked to these properties. Future approaches could be more technical than simply grinding and blending, allowing a better use of each cement component to achieve a lower CO2 intensity.

Evaluation of calcined coal slime in binary and ternary ordinary portland cement composites: The role of calcination temperature

Coal slime is a by-product of coal washing plants, which accounts for around 8.3% of total coal production. China generates about 200 million tons of coal slime annually, and most of which can not be utilized efficiently. As a result, the disposal of coal slime leads to serious environmental problems and high costs. To provide a green utilization of coal slime, this study investigated the preparation of binary and ternary cement binder systems by using various calcined coal slime particles. The effects of calcination temperatures (600 °C, 700 °C, 800 °C, and 900 °C) on the evolution of mineral phases, microstructure and morphology of coal slime were addressed and discussed. The feasibility of calcined coal slime in blended cement preparation was tested and evaluated in comparison with calcined coal gangue. The results indicated that kaolinite in coal slime can be effectively transformed into metakaolin at 600 °C. The increase of calcination temperature after 600 °C reduced the reactivity, porosity and water demand of calcined coal slime. 600 °C Calcined coal slime effectively promoted the formation of monosulfate and the monocarboaluminate in binary and ternary cement, respectively, as well as the hydration process. The highest compressive strength of the calcined coal slime blended sample achieved 48.04 MPa, which presented a higher performance than the calcined coal gangue. The organic components in coal slime could be the key to reaching a high reactivity at a low (600 °C) calcination temperature. The calcined coal slime has the potential to be a reactive additive in cement-based materials.

FLEXURAL STRENGTH CHARACTERISTICS OF PAWPAW LEAF ASH AND BAMBOO LEAF ASH BLENDED CEMENT CONCRETE

This research focuses on flexural strength characteristics of pawpaw leaf ash and bamboo leaf ash blended cement concrete. Several tests were carried out, according to BS and ASTM requirements to determine the physical and mechanical properties of pawpaw leaf ash and bamboo leaf ash blended cement concrete, investigate the effects of curing age on flexural strength characteristics of pawpaw leaf ash and bamboo leaf ash blended cement concrete and examine the effects of percentage replacement of cement with pawpaw leaf ash and bamboo leaf ash blended cement concrete on flexural strength characteristics. A total of 60 cubes were cast, cured in water for 7, 14, 21 and 28days. Test results showed that the flexural strength of the concrete cubes increases with an increase in the curing age and decreases with increasing percentage replacement of cement with pawpaw leaf ash and bamboo leaf ash. The optimum replacement level of pawpaw leaf ash and bamboo leaf ash was obtained to be 5%. The study concluded that concrete containing the cement blends of cement and Pawpaw leaf ash and bamboo leaf ash at a replacement level of 5% is only recommendable for use in light concrete works construction.

Limestone powder, calcined clay and slag as quaternary blended cement used for green concrete production

Cement is among the most widely used building materials in recent years. In addition, the accumulation of massive waste has impacted the city's appearance. As a result, there was a need to reduce waste by using by-products from industrial waste to replace cement and reduce greenhouse emissions to produce mortar or concrete green that has good performance, environmentally and sustainably. This research study aims to design green concrete with the highest feasible replacement level with different cement content that satisfies fresh and mechanical characteristics used for structural application and eliminate negative environmental impacts simultaneously. The empirical work was conducted by preparing 12 blends to produce green concrete by substituting cement with three ratios of various by 30% (10% LMP +10% SS + 10% CC), 40% (10% LMP +10% SS + 20% CC), and 50%(10% LMP +15% SS + 25% CC) with three binder contents (355 kg/m3, 400 kg/m3, and 460 kg/m3). The mix design was carried out according to the American Concrete Institute (ACI) Code. Then environmental influences of green concrete blends were calculated by evaluating the declines in carbon dioxide (CO2) emissions. The results showed that adding limestone powder (LMP),calcined clay (CC), and steel slag (SS) as partial cement replacement decreased the slump properties of fresh concrete, so an increased dosage of superplasticizer (SP) in the fresh properties is needed. Green concrete containing quaternary cement by 30%, 40%, and 50% with SP dosage certain gave higher compressive, flexural, and splitting strength values at 90 days compared to normal concrete. However, UPV values indicate that all green concrete is of suitable quality. While water absorption has slightly increased in quaternary cement containing 50% for binder content 355, 400, and 460 kg/m3 increased by 4.2%, 2.7%, and 2.1%, respectively, compared with plain concrete. The evaluated reduction of carbon dioxide emissions study indicated that the green concrete, when increased in cement replacement percentages by up to 50% for binder content 355, 400, and 460 kg/m3 reduced CO2 emissions by 35.9%, 36.4%, and 37.1%, respectively. As a result, adopting the idea of green concrete is a promising strategy for reducing carbon dioxide emissions and conserving natural resources.

Effects of recycled mortar powder on the properties and microstructure of magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) has become a popular research topic owing to its rapid hardening and high early strength. However, its high carbon emissions and cost limit its large-scale applications. To reduce MKPC’s carbon emissions and preparation costs and to improve the resource reutilization of construction waste, we investigated the effects of the particle size and dosage of recycled mortar powder (RMP) on the setting time, mechanical properties, physical phase, and microstructure of MKPC. The results indicated that when the particle size of RMP increased from 30 to 66 μm, the setting time of MKPC increased from 10.5 to 13.1 min, and the compressive strength (at 28 d) decreased from 52.4 to 38.0 MPa. Therefore, increasing the RMP particle size can prolong the setting of MKPC and reduce its compressive strength. Additionally, increasing the dosage of RMP reduced the setting time of MKPC and promoted the development of compressive strength in later stages. When the RMP dosage increased from 0% to 40%, the setting time of MKPC decreased by 26.1%, and the compressive strength increased by 50.2%. According to the results of pore structure and microstructural analysis, the incorporation of RMP improves the microstructure of MKPC, significantly enhancing its mechanical performance. Therefore, RMP can be used as an economical and ecofriendly cement blending material to reduce the preparation cost of MKPC and the carbon emissions of the construction industry and improve the resource reutilization of construction waste.

Insight into the synergic effects of circulating fluidized bed fly ash, red mud and blast furnace slag in preparation of ultrahigh-performance concrete: Reaction mechanism and performance optimization

Ultrahigh-performance concrete (UHPC) is a kind of special concrete with excellent mechanical properties and good flexibility that has attracted much attention. Partial replacement of cement with supplementary cementitious materials (SCMs) can significantly reduce costs and ensure UHPC performance. The composite preparation of cementitious materials using the physicochemical properties of different solid wastes has been proved to be effective. On this basis, the highly alkaline solid waste red mud (RM), highly pozzolanic activity solid waste containing sulfate circulating fluidized bed fly ash (CFA) and high pozzolanic activity solid waste blast furnace slag (BFS) were utilized to prepare low cement clinker UHPC. 20 groups of experiments were designed by response surface methodology (RSM). Then, the optimization and prediction of the performance of low cement UHPC was explored using simplex lattice method. In addition, the hydration degree and pore structure were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury intrusion porosimetry (MIP) and back scattered electron (BSE). In the case of 60% cement blending, the best compressive strength (128.15 MPa) occurred in 9% CFA, 28% RM and 3% BFS. The results demonstrated that the increasing strength existed with the addition of RM and a high content of CFA had a negative impact on performance development. In the cases of low cement systems (<45%), however, the compressive strength increased and then decreased as CFA content increased from 0 to 40% or RM content increased from 0 to 70%, which meant that a compound synergistic existed among the three solid wastes. Microstructure analysis demonstrates that the hydration degree and pore structure of UHPC were effectively improved due to synergies among CFA, RM and BFS. These results implied that the compound synergy is more significant in low clinker systems and beneficial to the development of strength. This paper provides a reference for low cement clinker and the low-cost preparation of UHPC.

Study of microstructural changes in blast-furnace cement hardened by repeated dry and wet curing at high temperatures

In ordinary hardened cement, the pore structure changes with microstructural changes due to repeated dry and wet cycles. However, the calcium-silicate-hydrate (C-S-H) produced in blended cement is different from that of ordinary cement because blast furnace slag and fly ash are used in blended cement. In this study, microstructural changes in ordinary cement and hardened blast-furnace cement, which have different compositions of C-S-H, due to repeated dry and wet cycles at high temperatures, were analyzed by solid-state nuclear magnetic resonance (NMR) for structural changes in the products, and by time domain NMR and mercury intrusion porosimetry for changes in moisture and pore structure in the hardened cement. As a result, it was confirmed that the degree of coarsening of capillary porosity in blast-furnace cement was lower than in ordinary cement due to drying and repeated dry-wet cycles. This is believed to be because the aluminum contained in the blast furnace slag of the blast-furnace cement, which is present in the interlayer, improves the resistance of the C-S-H layer to compaction, resulting in less change in the pore structure. This study is expected to contribute to fundamental research on hardened cement in the future.

Performance evaluation of ternary blended cement concrete partially replacement of natural sand with granite quarry dust

Cementitious composites are the most frequently used man-made material, with a 25 billion tonne manufacturing volume and 5% greenhouse gas emissions. Concrete composites release a lot of CO2 into the environment. Thus, replacing concrete composite raw material is a priority. To reduce this industry's carbon footprint, large-scale reuse of industrial byproducts, including Fly Ash (FA), Silica Fume (SF), and Ground Granulated Blast-Furnace Slag (GGBS) in cementitious composites, is growing. This method addresses the waste management for industry byproducts in two ways. The mechanical strength and durability of cementitious composite products with many ingredients must be recognised. This study's major goal is to evaluate high-strength cementitious composites' mechanical strength and durability. FA (20%, 30%, and 40%), SF (5%, 7.5%, and 10%), and GGBS (10%, 15%, and 20%) binder were used to make high-strength cementitious composites. Waste management has developed into a problem for the environment. The illegal and unethical practices involved in mining natural river sand (NRS) have gotten worse. Therefore, by substituting Granite Quarry Dust (GQD) for fine aggregate, the lack of NRS for a building is prevented. GQD was employed to replace natural river sand at different levels of replacement as the fine aggregate phase in 10%, 20%, and 30%. The fresh cementitious composites properties were evaluated, strength properties such as compressive strength, flexural strength, and split tensile strength were also evaluated and additionally, the durability characteristics such as water sorptivity and the Rapid Chloride Permeability Test (RCPT). We shall evaluate it with normal concrete based on the results.

Effect of C-S-H-PCE and TEA on performances of lithium slag-cement binder

In order to promote rheological behavior and strength enhancement of lithium slag-cement binder at early age, synergistic adoption of synthetic calcium silicate hydrates (C-S-H)/polycarboxylate (PCE) and triethanolamine (TEA) into lithium slag-cement binder was conducted. The rheological performance, setting behavior, hydration process and microstructure of blended cement were analyzed. The results showed that the adoption of C-S-H-PCE improved the rheological behavior of fresh binder, shown as decreased viscosity and yield stress. The addition of TEA weakened the rheological behavior of fresh binder, shown as elevated viscosity and yield stress. Both C-S-H-PCE and TEA accelerated the hydration process of lithium slag-cement composite binder, shortened the setting time, and promoted compressive strength enhancement at early ages. C-S-H-PCE provided nucleation sites for early hydration products of silicates, while TEA generated the transformation of AFt to AFm. The synergistic action of C-S-H-PCE and TEA accelerated the formation and growth of hydration products, and hence contributed to more compact and dense microstructure of hardened matrix.

Expansion and Mitigation of Alkali-Silica Reaction in Binary Blended Concrete Confining Potentially Reactive Aggregates

Without a cure but preventable, Alkali-Silica Reaction (ASR), dubbed the “Concrete Cancer,” happens when alkali in cement bonds with silica in aggregates to form an expansive gel. This research aims to investigate expansion and influence mitigation of ASR in concrete by identifying potentially reactive aggregates causing its onset and using binary blended cement to slow down unwanted gel expansions through the mitigative ability found in its fly ash component. This research also observed variations in expansive behavior and the physical changes that arose after the experiments. Aggregate samples were collected from different quarries in Davao, Philippines, denoted as Deposit A, Deposit B, Deposit C, and Deposit D. These deposits were tested according to the ASTM C1260: Accelerated Mortar Bar Tests (AMBT) to identify a reactive group. Three aggregate groups, Deposit A, Deposit B, and Deposit C, were tagged as reactive due to exhibiting more than a 0.1% increase in lengths, indicating unideal expansion. Additional sets of AMBTs were done for the identified aggregates using blended cement as a binder to test the combinations' ability to minimize expansion. This resulted in an average expansion decrease per set of approximately 78%, 82%, and 85% for A, B, and C, respectively, further strengthening the reputation of fly ash as an effective mitigating SCM against ASR.

Hydration and phase evolution of blended cement composites containing lithium and saturated metakaolin

Although the high efficiency of coupled lithium and saturated metakaolin in alkali-silica reaction mitigation has been documented, its influence on cement hydration remains uninvestigated. In this study, saturated metakaolin with varying degrees of saturation and its combined influence with lithium on the hydration kinetics, phase evolution, and development of microstructure and molecular structures of hydration products in the blended cement composite was investigated. The experimental and thermodynamic modeling results indicate the synergistic effect between saturated metakaolin and lithium in enhancing the hydration of cement, interaction between metakaolin and cement, incorporation of Al in the silicate chains, and precipitations of Al-rich phases. In the blended cement matrix, the dissolution of metakaolin, formation of calcium silicate hydrates with incorporated aluminum (C-(A)-S-H), and precipitation of strätlingite are improved by 19.6%, 17.6%, and 20.0%, respectively, and the formation of cubic siliceous hydrogarnet was triggered.

Volcanic ash from La Palma (Canary Islands, Spain) as Portland cement constituent

The last volcanic eruption on the island of La Palma (Spain) took place in 2021. Significant activity started in September of that year with the vigorous emission of volcanic gases and ash and lasted for three months. It is estimated that the Cumbre Vieja volcano emitted more than ten million cubic meters of ash comprising pyroclastic materials like those found in many parts of the world. Some of these volcanic ash deposits are untapped, despite their potential construction industry applications. Since the chemical composition and mineralogy of the ash depends on the type of magma from it originates, this paper characterizes this material and evaluates its suitability as a major constituent of Portland cement. This volcanic ash is rich in silica (45%) and alumina (15%), meaning it reacts with portlandite. The blended cements with up to 40% replacement content meet the standardized chemical, physical, and mechanical requirements and present good intrinsic durability values (resistivity and capillary absorption), making them viable for the manufacture of low-carbon-footprint eco-cements. This paper seeks to provide society with lasting technical, environmental, and social benefits through recovery of this ash.

Durability evaluation and environmental implications of blended cement with colloidal nano-silica for use in recycled fine aggregate concrete: Experimental and theoretical study

The incorporation of waste materials in concrete is currently a practical solution to solve certain environmental concerns. Because of the property degradation of the produced concrete owing to the addition of waste materials, using pozzolans in the concrete mix can help improve the mechanical performance of recycled concrete. Therefore, in this research, the mechanical specifications of recycled concrete were evaluated at different volume fractions of recycled fine aggregates (RFA) replacing natural fine aggregates (NFA). In addition, the impact of adding colloidal nano-silica particles on the performance of conventional and recycled concretes was investigated. Various parameters comprising compressive strength, pulse velocity, splitting tensile strength, flexural strength, elastic modulus, and water absorption were carefully examined. The attained experimental results reveal that the mechanical and physical characteristics of concrete degrade with increasing the volume fraction of RFA replacing NFA. Also, increasing the weight percentage of nano-silica replacing cement up to 6% in conventional concrete and that containing RFA improves the mechanical and physical properties, the optimum percentage of which was determined as 4.5%. Furthermore, relationships were recommended for predicting the compressive, splitting tensile, and flexural strengths as well as the elastic modulus of concrete mixes by including the RFA and nano-silica replacement levels, which are in acceptable accordance with the experiments in the present study and those available in the technical literature. Finally, to investigate the environmental effects of recycled concrete with different RFA substitution levels and colloidal nano-silica incorporation, the problem-based CML 2000 and the damage-based IMPACT2002 + methods were applied using SimaPro9 software. Thus, environmental parameters such as acidification, global warming potential (GWP), eutrophication, natural resources, ecosystem quality, and human health were inspected. Subsequently, the GWP results were compared and presented using the CML 2000 and the Intergovernmental Panel on Climate Change (IPCC) approaches. To verify the estimates, all the attained results were examined against those captured from the Building for Environmental and Economic Sustainability (BEES) method. Findings show that despite the implementation of different unit measurements in different methods, the environmental effects in the CML 2000 and BEES methodologies are almost the same, suggesting that nano-silica is a raw material with the greatest environmental impact. Additionally, based on the life cycle comparison results of manufacturing one cubic meter of concrete with different mix designs using the damage evaluation approach, IMPACT 2002+, concrete with the RF0NS6 mix design triggered the highest damage extent in natural resource, climate change, ecosystem, and human health categories, respectively. This study fills a significant research gap from an environmental perspective by comprehensively investigating the durability and mechanical specifications of concrete containing RFA and nano-silica pozzolan. The findings presented in this research provide valuable insights into the realm of sustainable construction practices, paving the way for novel advancements in concrete technology.

Effect of Al2O3 content in slag on the relationship between slag reactivity and carbonation resistance

To understand the influence of slag chemistry on the carbonation resistance of slag-rich cement, this paper explored the carbonation characteristics of blended cement systems with different Al2O3 contents in slag through accelerated carbonation test. Irrespective of slag chemistry, three main CO2 binding phases were identified during accelerated carbonation test, i.e. carbonated Ca-Al AFm phases (amorphous or nano-crystalline), carbonated hydrotalcite-like phase, and calcium carbonate (amorphous calcium carbonate, vaterite, and calcite). Additionally, it was noted that the classification employed for slag reactivity (based on slag chemistry) cannot be extended to predict carbonation resistance of slag-rich cement directly. The main challenge occurred for slag with high alumina content. The experimental results showed that Al2O3-rich slag exhibited a high reactivity and can be considered as a reactive component in the blended mixture; however, it did not contribute to carbonation resistance of the mixture. Especially for CO2 binding capacity, it was similar for systems with varied alumina content in slag (from 3.69 to 18.19 wt.%) in the completely carbonated area.

Cold Water Extraction for determination of the free alkali metal content in blended cement pastes

In this work, Cold Water Extraction (CWE) was performed on blended cement pastes to extract the pore solution and determine the free alkali metal content. To better understand CWE results, the reactivity of cementitious materials was also investigated, complemented by TGA and quantitative XRD analysis. The study aimed at being generic to assess the suitability of the methods, and included 9 SCMs with various compositions: limestone, coal fly ash, two calcined clays, two biomass ashes, sewage sludge ash, crushed brick and glass beads.The study highlighted the importance of assessing the reactivity of SCMs in parallel to performing CWE, as this contributes to a more certain interpretation of the results. In general, results obtained with CWE were consistent with the existing literature about the effect of binder composition on the free alkali metal content. From a practical view, CWE and SCM reactivity tests could be performed with basic laboratory equipment and appeared to be applicable to both traditional and alternative SCMs.

Enhanced cement formation for well completion in gas hydrates reservoirs

Natural gas hydrates (NGHs) have abundant reserves and are greener energy source compared to petroleum resources. Intense heat release of cement slurry impacts the stability of NGHs during oil well cementing operations. Conventional low hydration-heat cement slurries significantly reduce the early-stage strength. In this paper, a novel strategy to optimize the exothermic and mechanical properties of cement slurry is proposed with the synergistic effects of various mineral admixtures and additives. The hydration heat and microstructure of cement with different admixtures were studied through isothermal calorimetry (IC), semi-adiabatic temperature test (ST), scanning electron microscopy (SEM), X-ray diffraction (XRD) and mechanical strength tests. The results indicate that the addition of nanosilica (NS) and C–S–H seeds lead to high early-stage strength for cement slurry substituted with high-volume fly ash (FA) and ground granulated blast furnace slag (GGBS), which meets the engineering performance for NGHs cementing. Compared with neat cement, blended cement designed with the new strategy has a 40.46% lower cumulative heat and a 56% higher compressive strength after 24 h. However, ST showed that the separated hydration heat rate peaks recombine together at higher temperature. The thermal storage performance of solid-solid phase change material (SSP) can effectively control the temperature rise due to cement hydration and maintain the separation of hydration heat rate peaks. This study provides novel ideas for the construction of low hydration heat and high early-stage strength cement slurry, and also provides key theoretical and methodological support for the performance control of cement slurry for NGHs cementing.

Resistance of ordinary and low-carbon cements to carbonation: Microstructural and mineralogical alteration

The rising demand for green construction materials has led to tremendous research efforts towards the development of low-carbon cements, although their carbonation resistance is expected to be lower than that of ordinary Portland cement (OPC). This study aims to assess the carbonation resistance of various cements by thoroughly investigating the changes in the microstructure and mineralogy under accelerated carbonation conditions, which have not been comprehensively described in the literature, especially for blended cements. Two types of materials were investigated: cement pastes made from type CEM I and III cements and mortars with the same water/cement ratio of 0.55. Various analytical techniques have been used to examine microstructural and mineralogical alterations as a function of carbonation duration. It was demonstrated that CEM III cement pastes exhibited the fastest carbonation rate, whereas CEM I cement pastes had the largest CO2 uptake owing to carbonation. The mass change of carbonated materials and the carbonation depth were found to be well correlated. Overall, carbonation refines the microstructure, resulting in a significant decrease in water sorptivity, although an increase in the specific surface area and micropore volume was observed, indicating the opening of gel pores due to carbonation, which is more pronounced for CEM III materials. Additionally, this study allows a qualitative assessment of the extent in alteration of C-(A)-S-H gel structure and bound water of CEM I and CEM III materials.

Recycling and valorization of hydrated cement blends in mortars via semi-dry carbonation – The role of waste glass, granulated blast furnace slag and fly ash

The recycling technology of demolished concrete wastes in building materials manufacture provides a possibility of achieving sustainable constructions. Carbonation pre-treatment helps to enhance the performance of recycled concrete fines effectively. To investigate the effects of semi-dry carbonation on the utilization of recycled concrete fines containing supplementary cementitious materials (SCMs) in new concrete production, recycled blended cement paste powder (RBCPs) containing granulated blast furnace slag (GBS), fly ash (FA), or recycled glass powder (RGP) were prepared in the lab. The performance of mortars produced by carbonated recycled blended cement paste powder (C-RBCPs) and RBCPs blended cement were evaluated. C-RBCPs exhibited superior performance in workability and mechanical properties of prepared mortars compared to carbonated OPC powder. The results indicated that the RBCPs exhibited a lower carbonation degree (less than 53.4%) and CO2 uptake compared to OPC samples due to the lack of available Ca in the originally blended cement after incorporation of GBS, FA and RGP. As the main carbonation products, calcite, aragonite, and vaterite were all observed in C-RBCPs, the category of SCMs exhibited visible influences on the crystal format of calcium carbonate, as well as the reactivity of C-RBCPs in blended cement mortars. Overall, the semi-dry carbonation can promote the reactivity of C-RBCPs efficiently. The effects of the SCMs category should be considered in the recycling processes of cement wastes. The application of GBS, FA, and RGP in blended cement can help to achieve excellent sustainability of C-RBCPs blended mortars after semi-dry carbonation pre-treatment..

Enhanced autogeneous self-healing of MgO blended composites incorporating with silica fume

Many studies have been conducted on the autogeneous self-healing either using pozzolan or MgO approaches. It is well accepted that MgO adversely affects strength development particularly at an early age. Nevertheless, MgO is well accepted mineral admixture that has a promising self-healing ability for cement-based composites. Numerous efforts have been conducted in overcome the shortcoming of the strength of cement composites due to MgO. Various findings and studies have shown that incorporating MgO with pozzolans can be detrimental to the strength of cement composites; this includes any cement-based material that is incorporated with MgO. Thus, it is necessary to evaluate an appropriate blended cements in combination with MgO that possesses a self-healing ability without compromising its strength development. The study evaluated autogenous self-healing of magnesium oxide (MgO) blended mortar containing silica fume. 5% silica fume was applied into 5%MgO blended cements and for systematic analysis, effect of each single binder was also evaluated independently. A single crack was fabricated at 7-day and then, the healing ability was evaluated based on flexural strength test, crack sealing and microstructural analysis. Furthermore, ANOVA was employed to evaluate the significance of enhancement method to the MgO blended cement. The finding indicated that silica fume slightly enhanced self-healing of mortar. Similarly, statistical analysis confirmed that the autogenous self-healing of MgO cement is more pronounced with the addition of silica fume.

Hydration, mechanical and transfer properties of blended cement pastes and mortars prepared with recycled powder or limestone filler

The fine fraction (<80 μm) of recycled aggregates from construction and demolition wastes, currently considered as waste, is investigated as a candidate mineral additive for partial replacement of Ordinary Portland Cement (OPC) to reduce the environmental impact of cementitious materials. Although recycled powder could affect hydration reactions due to the presence of residual anhydrous cement particles and to its high specific surface area, very few studies are available in literature concerning these aspects. Cement pastes and mortars prepared with 0%, 10%, and 20% replacement by weight of OPC by either Recycled Powder (RP) or Limestone Filler (LF) are compared in terms of hydration degree, mechanical and transport properties using several techniques, including Isothermal Calorimetry (IC), Thermogravimetric Analysis (TGA), water porosity, mercury intrusion porosimetry and gas permeability. The results revealed that mixtures blended with RP or LF have a similar decrease in the overall hydration degree compared to the hydration degree of pure OPC mixture due to a dilution effect, although both additives have a small reactivity. A moderate increase in porosity and intrinsic permeability with the replacement rate is observed. Pastes and mortars blended with RP have a compressive strength and a Young modulus nearly identical to those with the same amount of LF, despite RP having worse properties than LF. A multiscale micromechanical model is established and reproduces faithfully these experimental results for the elastic moduli, based on the simplified assumptions that LF is nearly inert while RP reduces the effective water to binder ratio by both absorption of water and internal hydration reactions.