Portlandite Content Research Articles

An assessment of the pozzolanic potential and mechanical properties of Nigerian calcined clays for sustainable ternary cement blends

This study investigates the potential of calcined clays from Nigerian deposits as supplementary cementitious materials. Clay materials were obtained from three sites namely: Ikpeshi, Okpilla and Uzebba. The raw clay samples were then calcined at 700°C and 800°C. Chemical and mineralogical compositions were determined for the raw and calcined clay samples using XRF and XRD respectively. The chemical composition by XRF confirmed these clays as potential pozzolans with SiO2, Al2O3, and Fe2O3 collectively exceeding 70%. XRD analysis identified kaolinite and quartz as major mineral phases in the raw clays, which transformed into metakaolin upon calcination. Thermo Gravimetric Analysis (TGA) indicated varying lime consumption levels among the clays, with Ikpeshi clay displaying the highest pozzolanic reactivity and Uzebba clay the least. Compressive strength investigation on mortar cubes prepared with 50% substitution of Portland cement with the calcined clay and limestone, showed that Ikpeshi clay at 800°C had the best strength performance, with strength activity index of 0.92 (at age 28 days), demonstrating superior pozzolanic potential. Strength development was more significant between 7 and 28 days, indicating the pozzolanic reaction's contribution to long-term strength. However, initial strength at 3 days was lower than the reference Portland cement due to a delayed pozzolanic reaction. XRD analysis of blended pastes revealed typical phases of hydration like portlandite, calcium silicate hydrate phase, strätlingite, and ettringite, with the calcined clay blends showing reduced portlandite content, indicating absorption by the pozzolan's alumina phase.

Influence of alkali metal formates and calcium formate on workability, hydration and basic properties of reactive powder concrete

AbstractThis work aims to study whether it would be possible to use alkali metal formates and calcium formate in order to increase the workability of reactive powder concrete (RPC) and how these additives affect hydration, mechanical properties and mineralogical composition of RPC. These substances were added together with superplasticizer. Therefore, paper deals with possibility of increase in workability which would be higher when compared to the sole addition of only the superplasticizer themself. The effect of alkali metal formates and their replacement with calcium formate on slump flow, mechanical properties and pH of RPC was studied. Furthermore, the influence of potassium formate and its replacement with calcium formate and with calcium oxide on the hydration of RPC was observed with the help of isothermal calorimetry and thermal analysis. The results showed that the addition of studied compounds allows to achieve an increase in RPC slump flow. However, it is necessary to add these substances in an optimal ratio of alkali metal formate/calcium formate because a higher content of calcium formate leads to a decrease in slump flow. For ideal ratios, the compressive strength after 90 days is still above 218 MPa and the flexural strength is still above 23 MPa. In calorimetric measurements, it was observed that the addition of potassium formate leads to a decrease in the total amount of heat developed in the induction period. According to thermal analysis, additions of the studied additives to RPC caused changes in the content of portlandite and calcite.

Sustainable utilization of phosphorus-rich sludge in cement composites: Multiscale evaluation and mechanistic analysis

The treatment of sludge poses challenges for resource utilization and environmental protection, and utilizing sludge as supplementary cementitious materials (SCMs) presents a viable solution. However, the phosphorus content significantly influences the cement hydration process. This study primarily investigates the feasibility of phosphorus-rich sludge (PRS) as SCMs and examines the effects of combining PRS with calcined clay on cement hydration. The research focuses on hydration heat, mechanical properties, microstructure, and durability of composites comprised of PRS, limestone, calcined clay, and ordinary Portland cement. The results indicate that PRS delays early hydration reactions, leading to a decrease in early compressive strength; after 7 days, the compressive strength is approximately 14.3 MPa (sample S20C10L15). However, over time, the strength increases to 34.1 MPa at 28 days, reflecting a 138.5 % increase compared to the 7-day compressive strength (with sample OPC exhibiting only 69.1 %). This correlates with the hydration exothermic peak occurring in the later stages and the transition of phosphorus's effect on cement hydration from inhibitory to non-inhibitory. The phosphorus in PRS partially replaces silicon atoms in C-(A)-S-H gel, forming C-S(A,P)-H gel. This process refines pore sizes within PRS cementitious materials, enhancing compressive strength over time. Early hydration inhibition and the subsequent pozzolanic reaction of PRS reduce portlandite content, which lowers carbonation durability and thermal expansion coefficient. However, the quaternary blend of PRS, limestone, calcined clay, and ordinary Portland cement demonstrates excellent mechanical properties. This study provides experimental evidence for reducing the environmental impact of PRS and exploring carbon reduction strategies in the cement industry.

Combined effect of self-stressing and confinement on GFRP-LC3 interface bond

The load capacity, failure mode and durability of reinforced concrete members are strongly affected by the bond strength between the concrete and the reinforcement. This work presents a physics-based approach to improve the bond strength based on self-stressing effect. Combination of limestone calcined clay cement (LC3) and calcium sulphoaluminate cement (CSA) with different ratios was employed to develop self-stressing function. The addition of CSA induces a remarkable volume expansion of matrix due to the formation of ettringite, it however leads to a decreased compressive strength because of the reduced Portlandite content and increased porosity. A push-out test was conducted to evaluate the interface properties between glass fiber reinforced polymer (GFRP) and LC3-based matrix. The results show that the interface bond strength is highly dependent on the matrix strength under unconfined condition. On the contrary, under confined condition, the interface bond strength increases linearly with the expansion value regardless of matrix strength, attributed to that the self-stressing effect can effectively refine the matrix pores and densify the interface transition zone. The findings from this work demonstrate that the self-stressing effect holds promise to be a plausible method to strengthen the overall properties of reinforced concrete without creating additional carbon emission.

Power ultrasound-assisted enhancement of granulated blast furnace slag reactivity in cement paste

This paper introduces a first-time investigation into the impact of power ultrasound (PUS)-assisted preparation on the physicochemical and mechanical properties of cement-granulated blast furnace slag (GBFS) composite pastes. Pastes containing deposited GFBS with varying particle size fractions, partially replacing Portland cement, were prepared using PUS (ultrasonic horn tip, 20 kHz, 700 W) in pulse mode in a vertical jacketed glass sonoreactor with closed-circuit cooling. Cement paste incorporating 20 wt.% GBFS as mass substitution with varying particle size fractions was characterized by several physicochemical techniques at different curing ages. Exploring the cement and GBFS interaction induced by PUS, the compressive and flexural strength, the elastic modulus and indentation hardness, the heat of hardening, the mineral composition of hydration products, and the specific surface area BET were evaluated for a curing time of up to 28 days. The grain size distribution of GFBS and the reaction mixture's pH were measured. Both mechanical properties, heat of hydration and nanoporosity exhibited strong sensitivity to PUS treatment. Sonofragmentation of GBFS particles (especially the 125–250 μm fraction) increased with increasing sonication time, resulting in a relative increase of fraction <63 μm and a decrease of fraction >125 μm by 275 % and 60 %, respectively. Using the obtained SEM-EDS data, a simplified mechanism is proposed to explain the effects induced by PUS treatment.

Evaluating the pozzolanic activity of andesite and calcined marl for high-performance concrete: a valorization of algerian mineral resources

This study evaluates the pozzolanic activity of andesite and calcined marl sourced from Algeria for potential use as supplementary cementitious materials. The research addresses the need for sustainable construction practices by leveraging local mineral resources. The objectives include assessing the pozzolanic properties of these materials and their effects on mortar mixes. The methodology involves collecting samples from specific quarries, crushing and grinding them into fine powders, and calcining the marl at 750°C. The materials were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). Pozzolanic activity was evaluated through Frattini and Saturated Lime Tests, followed by mortar mix analyses with varying substitution levels. Results indicated that andesite and calcined marl exhibit significant pozzolanic activity, with andesite showing the highest reactivity. The inclusion of these additives improved the formation of calcium silicate hydrate (C-S-H) and reduced portlandite content, enhancing the durability and mechanical properties of the mortar. The study concludes that these local mineral resources are viable alternatives to conventional cementitious materials, promoting sustainability in the construction industry.

Mechanical and fracture properties of mortars reinforced with glass fibre and prepared with different cement types

PurposeThe main aim of the current study is to investigate the effect of Anti-Crack HP 67/36 glass fibre on the mechanical performance of mortars made of cement, with a focus on post-cracking evaluations using the digital image correlation (DIC) technique.Design/methodology/approachExperimental tests were carried out on 36-mm long fibres at 0.8% by volume and added to the normal strength (NSM), high strength (HSM) and high strength mortar with fly ash (HSMFA) mortars. CEM I 52.5 CP2 NF, CEM II/A-L 42.5 NF and CEM III/C 32.5 N-SR PM were used for each series of mortar to assess the performance of the glass fibres with the types of cement. F-class fly (FA) ash was used to reduce global CO2 emissions.FindingsThe mortar’s strength decreased as the cement types changed from CEM I to CEM II and III. However, due to changes in the portlandite content of the cement, water porosity increased for both types of mortar, without and with fibre. It was also found that using glass fibre increased flexural strength more than compressive strength, regardless of the type of cement used. For all the strength classes, it was found that the mortar mixes with CEM I had the highest critical crack opening (wc) and fracture energy (GF), followed by CEM II and III. No significant effects were observed in the mortar’s property by replacing fly ash (12%).Research limitations/implicationsOnly mortars were formulated in this study, but the results must be verified at the concrete scale.Practical implicationsValidation of the DIC technique to characterize the post-cracking behaviour of cement-based material. Use of glass fibres to improve the material’s resistance to cracking.Social implicationsUse of CEM II and CEM III cements with low CO2 footprint instead of CEMI without altering the mechanical performance of the material.Originality/valueThe work is a further contribution to studying the cracking behaviour of several series of variable mortars depending on the resistance class and the type of cement used.

The improvement on calcium leaching resistance of high SCMs content cement in ammonium chloride solution using particle gradation technique

Particle gradations of Portland cement (PC), fly ash (FA), and blast furnace slag (BFS) were optimized to improve the calcium leaching resistance of blended cement with high contents (up to 70%)of supplementary cementitious materials (SCMs). The results showed that optimized blended cement showed refined initial pore volume distribution, reduced portlandite (CH) content, finer CH macrocrystals and enhanced stability of C-(A)-S-H gel. Consequently, it displayed exceptional calcium leaching resistance with reduced losses in mechanical performance, mass and pore degradation after calcium leaching. Blended cement with 30% PC (D50 = 14.46 μm), 30% FA (D50 = 10.94 μm), 20% BFS (D50 = 10.52 μm), 13% BFS (D50 = 5.31 μm) and 7% BFS (D50 = 4.71 μm), showing compressive strength retention rate of 79.05% and mass loss rate of 1.64%, was suggested as viable choice for calcium leaching resistant concrete.

Steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder under natural and accelerated marine environments

This study aims to investigate steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder. The chloride diffusion coefficient and compressive strength of concrete, and weight loss of steel were measured after the specimens were exposed to the tidal zone in a real sea environment for 1 and 2 years. The depassivation time of the embedded steel and the critical chloride content of the concrete under an accelerated marine environment were investigated in the laboratory. The test results revealed that the coefficient of chloride diffusion and critical chloride content of concrete and weight loss of steel decreased with increasing calcined kaolinite clay contents. Although utilizing calcined kaolinite clay in concrete mixtures reduced critical chloride content (0.655% by wt. of binder for OPC and 0.573 to 0.427% by wt. of binder for C15 to C45) because of the lower portlandite content, it caused a longer rebar depassivation time (46 days for OPC and 63 to 237 for C15 to C45). The ternary binder systems of cement, calcined clay, and fly ash demonstrated the best overall performances, i.e., the lowest chloride diffusion coefficient (0.29 ×10−12 m2/s) and the highest compressive strength of the concrete (38.7 MPa), and no weight loss of embedded steel at 2 years of exposure.

Durability and heavy metals leaching behavior of cemented paste backfill using chemical activated binary slag as binder under sulfate attack

The present study conducted an extensive investigation into the durability of Na2SO4-activated binary slag cementitious materials for use in cemented paste backfill (CPB) under sulfate attack conditions. The primary objectives were to assess the feasibility of employing a cost-effective and environmentally friendly binder in CPB applications. Samples were subjected to exposure to Na2SO4 and MgSO4 solutions for a duration of 30 weeks, and multiple aspects including dimension stability, micro and macro mechanical strength evolution, changes in phase assemblage, microstructure following sulfate attack, and heavy metals leaching were examined. The study revealed that Na2SO4-activated binary slag (OPC-slag/S) exhibited superior resistance to sulfate attack, demonstrating enhanced dimension stability. Notably, sample OPC-slag/S displayed an increase in compressive strength, even after prolonged exposure to sulfate solutions for 30 weeks. This increase amounted to approximately 10.76% and 4.81% following exposure to Na2SO4 and MgSO4 solutions, respectively. The heightened resistance of binder OPC-slag/S to sulfate attack can be attributed to its low portlandite content and the early consumption of aluminates, primarily due to the formation of ettringite. This phenomenon effectively prevents the formation of detrimental and expansive products within the cement matrix during sulfate attack. On the other hand, CPB samples with binder OPC-slag/S showed the best performance in heavy metals immobilizaton capacity due to the high resistance to sulfate attack. In conclusion, this study underscores the potential of utilizing OPC-slag/S as a cost-effective and environmentally friendly binder for CPB applications in sulfate-rich environments.

Evaluation of mechanical properties of cement mortars containing pond ash as partial replacement of river sand and prediction of properties by regression models

Despite vast research on the utilisation of coal ashes in cement mortars, many studies lack a comprehensive evaluation of properties related to mortar for masonry and plaster work. This study investigate properties like workability, compressive strength, drying shrinkage, tensile bond strength and adhesive strength through a systematic replacement of river sand by pond ash in cement mortars. Volumetric mix proportions of 1:3, 1:4, 1:5 and 1:6 (cement: sand) were considered, where river sand was replaced in the range of 20–100% by pond ash. At 30% pond ash content, properties like the compressive strength, tensile bond strength and adhesive strength improved in the range of 21–30%, 13–20% and 14–24%, respectively, for all mix proportions. At 60% pond ash content, these strength properties were comparable with those of control mixes and found suitable for mortars for masonry works. However, the drying shrinkage increased with an increase in pond ash content. At 30% pond ash content, drying shrinkage increased in the range of 26–40% for all mix proportions. The thermogravimetric analysis (TGA) showed that mixes with pond ash demonstrated reduced portlandite content compared to the control mixes, resulting in the formation of secondary C-S-H gel. Simple regression models were developed based on experimental results to establish the relationships between different properties. Based on coefficient of determination (R 2), variance inflation factor (VIF) and Durbin–Watson statistics, relationships between the strength and shrinkage properties were very well quantified to be used by researchers and practitioners. Utilisation of pond ash as partial replacement of river sand in mortars proved to be a useful step towards achieving circular economy at the same time reducing threat to depletion of limited natural resources.

Compressive strength ratios of concretes containing pozzolans under elevated temperatures

Cement production is one of the major pollution contributors owing to its large rates of energy consumption and gas emission. Moreover, high temperatures could detrimentally impact the concrete infrastructure and thus, it would be essential to study performance of such structures under exposure to the elevated temperatures. In this paper, post-heat performance of the concrete whose cement has been added by zeolite and bentonite at ratios of 6 and 10% (by cement weight) under exposure to temperatures of 28, 150, 300 and 700 °C, was studied. Based on the results, replacing cement by zeolite and bentonite at the age of 90 days under ambient temperature, increases the compressive strength compared to the control specimen. Moreover, it was observed that heating the cubic and cylindrical specimens containing 10% bentonite at 150 °C, increase the compressive strength by 40%. Conversely, the results indicate that when exposed to temperatures of 300 and 700 °C, a decreasing trend is seen in the tensile strength of both cubic and cylindrical specimens containing the pozzolans. Peak intensity of C–S–H has dropped as per rise in temperature from 28 to 700 °C. These values reveal that peak intensity of C–S–H up to 300 °C, is approximately the same but under 700 °C, it has reduced considerably. In all the cubic and cylindrical specimens, it can be seen that the specimens heated at 150° have the highest compressive strength and the specimens heated at 700 °C have the lowest compressive strength compared to the same unheated specimens. The XRD patterns at 150 and 300 °C, reveal decrease and increase in the Portlandite content the difference between conversion ratio of the cubic and cylindrical specimens in this study, to the values provided by the codes, is less than 10%.

An investigation on the physical properties of cementitious pastes modified with low dosage of waste glass powder and silica fume.

Portland cement (PC) production is among the industrial activities that most emit harmful gases. Its replacement to green binders turns into a timely issue to face the global restrictions due to climate changes. In this study, some properties of cementitious pastes prepared with waste packing glass powder (GP) and silica fume (SF) were characterized in line with a prefixed alkaline equivalent limit. These materials were obtained in Northeastern Brazil. Grinding operations used to produce GP into four size ranges ([45-75] µm, < 45 µm; [25-45] µm, < 25 µm) were disclosed. X ray diffraction showed that GP and SF substitutions did not change the hydration products commonly observed in PC pastes. The portlandite content measured with thermogravimetry was affected by GP size in both unitary and binary substitutions. The compressive strength measured after 56 days of curing was dependent on portlandite and void index contents measured in hardened pastes. Scanning electron microscopy coupled to energy dispersive spectroscopy were useful to show the effect of the particle size on the pozzolanic activity. It was found that 5% of PC replacement for GP < 25 µm was enough to raise the compressive strength by ~5%. For binary substitution, the strength increasing was ~ 20 %. The collectors of solid residues are the main players of waste glass recycling in Brazil. It is expected that the results of this study contribute to take out these workers from the fringes of the citizenship.

Comparison of the influence of the type of acidic environment on the properties of acid-resistant alkali-activated cements

The article is devoted to the study of acid resistance of materials developed on the basis of hybrid alkali-activated cements and includes the results obtained during previous studies focused in this direction. This directly concerns the composite compositions of the received cements.The relevance of the research is ensured by the need of the world market of building materials for modern, effective materials that will retain high acid resistance indicators along with increased physical, mechanical and technological characteristics. After all, as is known, traditional acid-resistant cements based on liquid potassium and sodium glass, although they provide appropriate values of resistance to the influence of an acidic environment, are extremely sensitive to the influence of water, which greatly reduces their service life. And materials based on Portland cement are generally not characterized by acid resistance due to the high content of portlandite (Ca(OH)2), highly basic calcium hydrosilicates and ettringite in the structure of hardened cement stone. That is why alkali-activated systems were chosen as the basis, the experience of working with them confirms the effectiveness of their use in the development of this research area.In the course of this study, a comparative characterization of the influence of the type of aggressive environment on the processes of structure formation of cement stone and the formation of acid-resistant phases is conducted. 5% solutions of hydrochloric (HCl) and nitric (HNO3) acids were used for the study. The obtained results not only confirm the possibility of using such cements in the conditions of an aggressive environment with a low pH, but also reflect the degree and influence of this type of environment on the material made according to the presented compositions. Thus, the compressive strength of the samples made according to these tested compositions after 90 days of exposure in hydrochloric and nitric acid solutions ranges from 43.1 MPa to 45.7 MPa and from 47.1 MPa to 49.7 MPa, respectively.

Thermodynamic Modeling of Sulfuric and Acetic Acid Attack on Hardened Cement Paste: Effect of Silica Fume

AbstractThe exposure of concrete structures to acid attack is a growing concern. This study employs thermodynamic modeling to investigate the changes in phase assemblage of powdered cement pastes subjected to a wide range of sulfuric and acetic acid concentrations. A modeling approach utilizing IPHREEQC implemented through Matlab is presented, and the obtained results are compared with pH measurements and compositions of equilibrated calcium and sulfate solutions. The influence of incorporating 11% silica fume (SF) as a replacement for cement predicted a 70% reduction of Portlandite content in the hardened cement paste. Consequently, the acid attack processes and subsequent pH reduction are affected. The modeling approach demonstrates good agreement with experimental data for acetic acid, across a broad range of acid concentrations, for both Portland cement and a blend with SF, without the need for any fitting parameters. However, significant discrepancies between the model and experiments are observed in the case of sulfuric acid. This discrepancy arises due to the formation of lump pieces of material in the experimental setup at higher acid concentrations. These lumps consist of a thin layer of altered hardened cement paste, primarily composed of sulfate‐rich phases, encapsulating unaltered hardened cement paste. Since the reaction was not homogeneous and the powder did not entirely react, the sulfuric attack experimental setup was not representative for validating the thermodynamic model.

Mix and measure - Combining in situ X-ray powder diffraction and microtomography for accurate hydrating cement studies

It is reported an innovative methodology based on in situ MoKα1 laboratory X-ray powder diffraction (LXRPD) and microtomography (μCT) avoiding any sample conditioning. The pastes are injected in 2.0 mm capillaries and the extremes are just sealed. The measurements take place in the same region of the hydrating paste. Thick capillaries are key to avoiding self-desiccation, which dictates the need of high-energy X-ray radiation for the diffraction study. This approach has been tested with a PC 42.5 R paste having w/c = 0.50. μCT data were collected at 12 h and 1, 3, 7 and 79 days. LXRPD data were acquired at 1, 3, 7 and 77 days. In this proof-of-principle research, the same paste was also cured ex situ. Portlandite contents obtained by thermal analysis, ex situ powder diffraction, in situ mass balance calculation and in situ powder diffraction were 13.8, 13.1, 13.1 and 12.5 wt%, respectively. From the μCT study, the grey value histogram evolution with time showed a crossing point which allowed us to distinguish (appearing) hydrated products from (dissolving) unhydrated cement particles. Segmentations were carried out by global thresholding and the random forest approach (one type of supervised Machine Learning). The comparison of the segmented results for the unhydrated cement fraction and the Rietveld quantitative phase analysis outputs gave an agreement of 2 %. The potential of this methodology to deal with more complex binders is also presented.

Alkanolamine-based chemically enhanced hydration reaction of ordinary Portland cement

This study aims to elucidate the origin of the improvement of mechanical properties of ordinary Portland cement (OPC) hydrates with the use of alkanolamine grinding agent (GA). It was found that the chemical activation induced by the use of 0.026 wt% GA led to improvements of the early strength as well as later strength. To be specific, GA predominantly enhanced ferrite (C4AF) hydration in both initial and later stages which resulted in more dissolution of calcite. As a result, the promoted ettringite formation at 1 day and monocarboaluminate (Mc) from 2 day were observed. Although the lower content of portlandite (CH) was found over the whole curing period due to the inhibition of CH crystal growth with GA, the amount of amorphous phase was higher from 1 day. More production of amorphous phase was most conspicuous during 7 to 28 days, which was possibly associated with more production of Fe-containing hydrates from the enhanced C4AF hydration.

Hydration, Reactivity and Durability Performance of Low-Grade Calcined Clay-Silica Fume Hybrid Mortar

Low-grade calcined clay, due to its low cost, availability and low temperature calcination, has been gaining attention in recent times as a supplementary cementitious material (SCM) in the manufacture of revolutionary building materials to improve the fresh and hardened properties of concrete. Silica fume, on the other hand, has been used, over the years, to improve the performance of concrete due to its reduced porosity and improved transition zone quality. In spite of the individual contribution of these two pozzolans to the strength and durability of concrete, there is a knowledge gap in the properties of ternary blended mixes utilizing calcined clay and silica fume. In this study, the synergistic effect of calcined clay and silica fume on the fresh and hardened properties of cementitious mortar have been investigated. The two pozzolans were used to partially substitute Portland cement to form a ternary blended composite binder having, at a maximum, a replacement of 30% by weight and a varying content of calcined clay and silica fume. The influence of the binary and ternary blended mixes on hydration, pozzolanic reactivity and the mechanical and durability properties of mortar was studied. From the results, partial replacement of cement with 30% calcined clay and silica fume caused significant reductions in the portlandite content of the two hydrated pastes at all curing ages. Drying shrinkage was found to be less severe in the control mortar than the blended cement mixes. Compared to the blended cement specimens, the control suffered the most weight (13.3%) and strength (10%) losses, as indicated by the sulphate resistance test.

Unraveling the Interplay of Physical-Chemical Factors Impacting the Carbonation Performance of Recycled Aggregate Concrete.

Recycled aggregate concrete (RAC) includes recycled concrete aggregates (coarse and/or fine) as substitutes for natural aggregates as an approach to achieving a circular economy. Some concerns remain about its performance, including the carbonation resistance. The higher porosity of recycled concrete aggregates is logically a disadvantage, but the analysis must address many other factors. This paper provides an in-depth examination of recent advances in the carbonation performance of RAC. The emphasis is on factors that influence CO2 diffusion and the carbonation rate, e.g., the replacement ratio, source concrete quality, interfacial transition zone features, residual portlandite content, and porosity. The influences of previous treatments, combined action with supplementary cementitious materials, and loading conditions are also discussed. The replacement ratio has a significant impact on the carbonation performance of concrete, but it is also dependent on other factors. During carbonation, the physical effects of the porosity of the aggregate and the physical-chemical effects of the portlandite content in the adhered mortar are particularly important. The residual portlandite is especially significant because it is the primary hydration product responsible for the alkaline reserve for carbonation and the potential pozzolanic reaction, which are per se competing factors that determine the carbonation rate.

Experimental investigations of aluminum hydroxide nanoparticles on properties of cementitious composites using macro and micro scale tests

The potential to use nanomaterials to produce high-performance cementitious composites is gradually developing. This study designed novel cementitious composites containing aluminum hydroxide nanoparticles (AHNPs), considering features such as amphoterism, functional groups, and compatibility with cement components. The percolation threshold of the AHNP dosage in cementitious composites was calculated as 0.5% by weight replacing cement, and cementitious composites containing 0.5% wt. AHNP have 1.11- and 1.94-fold greater compressive and flexural strength than plain cementitious composites, respectively. AHNPs increased the portlandite content and decreased the calcite content due to redox reactions and the formation of dmitryivanovite in the cement matrix. Compared with plain paste, the application of hybrid 0.3% wt. AHNPs and 0.1% wt. GO increased the compressive strength by 92.55%, flexural strength by 83.74%, fracture toughness by 5.29%, and calcite content by 35.38%. This combination also achieved increases of 72.38% in compressive strength, 18.23% in flexural strength, 10.91% in fracture toughness, and 5.18% in calcite content compared to cementitious composites modified with 0.1% wt. GO. GO and AHNPs generated a more compact structure due to their mutual hydrogen bonding capacity and thus enhanced the macro- and micro properties of cementitious composites by facilitating hydration.