Use In Cement-based Materials Research Articles

Use of nano-silica sol in concrete: Performance and influence mechanisms

Nano-silica sol (NSS) is an aqueous liquid containing colloidal nano-silica in dispersed state. It has been reported to offer better effects to the cement-based materials compared with nano-silica powder, which is by far the most widely studied nanomaterial for concrete applications. To identify the optimal type of NSS (acidic/ neutral/ alkaline) for use in cement-based materials, its effects on the performances and the influence mechanisms, a three-staged research program for testing the workability, strength, durability and chemo-physical properties of mixes with various types and contents of NSS at various ages has been completed. Generally, the addition of NSS decreased the workability and increased the strength and durability of concrete. It was found that alkaline NSS was the desirable type from the viewpoint of highest workability and strength. X-ray diffraction patterns, wet packing density, scanning electronic microscope images and mercury intrusion porosimetry tests verified the pozzolanic reaction effect, nucleation effect, densification effect and pore modification effect brought about by NSS. In-depth analysis revealed that the NSS induced nucleation effect at early age and pozzolanic reaction effect at later age, densified the microstructure and reduced both volume and size of pores. These effects explained the improvement of strength and durability of concrete by using NSS.

Waste Glass Utilization in Cement-Based Materials for Sustainable Construction: A Review

The construction industry has a significant environmental impact, contributing considerably to CO2 emissions, natural resource depletion, and energy consumption. The construction industry is currently trending towards using alternative construction materials in place of natural materials and cement, thereby reducing the environmental impact and promoting sustainability. Two approaches have been used in this review: scientometric analysis and a comprehensive manual review on the waste glass (WG) utilization in cement-based materials (CBMs) as a sustainable approach. Scientometric analysis is conducted to find out the current research trend from available bibliometric data and to identify the relevant publication fields, sources with the most publications, the most frequently used keywords, the most cited articles and authors, and the countries that have made the most significant contribution to the field of WG utilization in CBMs. The effect of WG on the mechanical properties of CBMs was found to be inconsistent in the literature. The inconsistent effects of WG impede its acceptance in the construction sector. This study intends to shed light on the arguments and tries to explain the opposing perspectives. This article summarizes the findings of various research groups and recommends new viewpoints based on the assessment of fundamental processes. The effect of utilizing WG on fresh and hardened properties of CBMs, including workability, compressive strength, split-tensile strength, and flexural strength, are reviewed. Furthermore, the microstructure and durability of composites containing WG are investigated. Different limitations associated with WG use in CBMs and their possible solution are reported. This study will assist researchers in identifying gaps in the present research. Additionally, the scientometric review will enable researchers from diverse regions to exchange novel ideas and technologies, collaborate on research, and form joint ventures.

Enabling high-strength cement-based materials for thermal energy storage via fly-ash cenosphere encapsulated phase change materials

The incorporation of phase change materials (PCMs) in cement-based materials opens pathways for large-scale thermal energy storage with tremendous opportunities for energy saving. However, traditional use of polymer micro-encapsulated PCMs (MEPCM) in cement-based materials lead to several well-known drawbacks (e.g., detrimental to mechanical performance, lower thermal conductivity, and high costs). In this research, a novel micro-encapsulation pathway is pursued, using fly-ash cenosphere to encapsulate PCMs for high volume use in cement-based materials. A comparative study was conducted to elucidate the effects of the cenosphere encapsulated PCMs (namely CenoPCM) and its polymer micro-encapsulated counterparts on the mechanical and thermal properties of functionalized cement-based materials. In addition, a micro-mechanics-based model was developed to predict properties of cementitious materials containing MEPCM. Property trade-off analysis shows that CenoPCM has substantial potential in the development of heat-storing cement-based materials, due to its significantly improved mechanical properties, good thermal conductivity, and much lower cost than other MEPCMs.

Screening of untreated municipal solid waste incineration fly ash for use in cement-based materials: chemical and physical properties

The environmental impact during concrete manufacturing can be reduced by using less cement or using types of cement with high amounts of secondary cementitious materials (SCMs) and fillers. Fly ash from municipal solid waste incineration (MSWI) is an unused material, which could potentially be used as an SCM or filler. The applicability of MSWI fly ash samples in cement-based materials was investigated through an indirect determination based on the chemical composition, toxic metal content and particle size distribution of the samples. Furthermore, how the samples compared to each other and how representative the samples were for MSWI fly ash, in general, were investigated by multivariate modelling. MSWI fly ash samples were obtained from Denmark, Sweden and Greenland. Comparing the chemical composition of the MSWI fly ash samples with the chemical requirements for coal fly ash to be used in concrete, specified in EN 450-1 2012, indicated a low potential as SCMs. Additionally, the MSWI fly ash contained and leached more toxic metals than the allowed limits. The particle size distributions were larger than cement and indicated limited potential as filler. A principal component analysis showed that the obtained samples were chemically different materials compared to each other and would have different effects if used in cement-based materials. Additionally, the samples from Denmark were unrepresentative of MSWI fly ash, while the Greenlandic and Swedish samples were comparable to previously studied MSWI fly ash samples.

Characterization of an Algerian natural pozzolan for its use in eco-efficient cement

The paper presents the characterisation of an Algerian natural pozzolan (NP) intended to for use in cement-based materials. The experimental programme was based on different tests on paste and mortar. The pozzolanic activity was assessed by the means of lime consumption over time of mixtures of lime-pozzolan (75% NP and 25% Ca(OH)(2), water-binder ratio of 0.45). The degree of reactivity was assessed by observing the crystallographic changes (XRD) and lime constumption (TG) up to 1 year of hydration. The effect of NP on cement-based mixtures was based on the measurement of the water demand and setting time of pastes, and on the compressive strength of mortars, up to one year. The replacement rates of cement by pozzolan were 5, 10 and 15%. A superplasticizer was used (0, 1, 2 and 3% of the binder mass). A calculation of the carbon footprint was investigated in order to assess if the natural pozzolan could be considered as eco-efficient when used in replacement of the clinker. The results showed that NP had a medium pozzolanic reactivity and with a medium-low silica content. The use of NP usually led to a small increase in the water/binder ratio (up to 10%) to maintain constant workability. The setting time was also increased by around 20%. Nevertheless, strength tests showed that the pozzolan had sufficient activity to counteract the water demand, since long-term compressive strength of the binary system (cement + pozzolan) were higher than those of cement alone. The use of NP in replacement of clinker involves a reduction in CO2 emissions for transport up to 1800 km, which is compatible with sustainable development. The results are most promising from both a performance-based and an environmental point of view.

Effect of curing time on granulated blast-furnace slag cement mortars carbonation

Currently, ground granulated blast-furnace slag cements use in cement-based materials is being increasing because perform well in marine and other aggressive environments. However, mortars and concretes made of this type of cement exhibit high carbonation rates, particularly in badly cured cement-based materials and when high blast-furnace slag contents are used. Concrete reinforcement remains passive but can be corroded if the pore solution pH drops as a result of the carbonation process promoting the reinforced concrete structure failure during its service life. Results show the very sensitive response to wet-curing time of slag mortars with regard to the natural carbonation resistance. Then, a minimum period of 3–7 days of wet curing is required in order to guarantee the usual projected service life in reinforced concrete structures. In this work, estimation models of carbonation depth and carbon dioxide diffusion coefficient in ground granulated blast-furnace slag mortars as a function of the curing period and the amount of ground granulated blast-furnace slag are proposed. This information will be useful to material and civil engineers in designing cement-based materials and planning the required curing time depending on their ground granulated blast-furnace slag content.

NATURAL AND CALCINED CLAYEY DIATOMITE AS CEMENT REPLACEMENT MATERIALS: MICROSTRUCTURE AND PORE STRUCTURE STUDY

This manuscript introduces clayey diatomite from Jelsovec deposit in Slovakia intended for use in cement and concrete industry. Jelsovec deposit contains 3350 kilotons of clayey diatomite to be easily mined. Natural clayey diatomite (CD) and calcined clayey diatomite (CCD) were used to substitute 5 to 15 % by wt. of CEM I according to EN 197-1 Standard. CCD was prepared from CD by calcination at 900 °C for 1 hour. Frattini test was applied for the estimations of pozzolanic activity. Pozzolanic activity of CCD is found to be comparable to that of traditional natural and industrial pozzolans. The pozzolanic activity of the CD is only slightly lower opposite to that of CCD. Both clayey diatomites are behaving as high-efficient pozzolans when partially substituting the Portland cement. Cement composites of Water/Solid ratio of 0.5 with a substitution rate of CEM I between 5 and 15 wt. % CD and CCD were used for the tests. The specimens were studied by X-ray diffraction and thermal analysis as well as mercury intrusion porosimetry after 28- and 365-days test on compressive strength. The composites consumed a larger amount of Ca(OH)2. They had a higher volume of gel-like hydrate phase and finer pore structure relative to the reference cement paste. The present findings indicate that Slovak diatomite from Jelsovec can be considered as a suitable pozzolan for use in cement-based materials. The results show that the microstructural properties of the respective materials are comparable to those of the traditional natural and industrial cement modifiers. Moreover, the substitution of CEM I by CD and CCD save energy and protect the environment by reducing the CO2 emissions.

Pozzolanic properties of fine and coarse color-mixed glass cullet

Mixed glasses of different colors are economically difficult to reuse for the fabrication of new glass products but their use in cement-based materials is a promising way to recycle this material. This paper deals with the pozzolanic activity of mixed glass cullet, by evaluating the pozzolanic behavior of a large range of glass particle sizes, from less than 40 μm (540 m 2/kg) up to 2.5 mm (2.2 m 2/kg). Five different classes of glass are assessed separately, in terms of compressive strength tests on mortars, consumption of lime (TG), morphology (SEM) and composition of hydrates (EDX and X-ray fluorescence). The results show that the pozzolanic activity increases with glass fineness and that, compared to a reference material without glass, equivalent or superior compressive strength can be obtained when using up to 40% of glass of 540 m 2/kg fineness. A transition fineness around 30 m 2/kg (140 μm) is highlighted, for which the pozzolanic activity becomes substantial. However, a slight but significant pozzolanic activity is detected for coarse particles (>1 mm), as confirmed by the consumption of Ca(OH) 2, the formation of C–S–H-like hydrates and an increase of 10% (5 MPa) in the compressive strength compared to an inert admixture. The chronology of the reaction (pozzolanic and alkali-reactive) for coarse glass particles is discussed.

Enhancing value of local materials in developing countries

ABSTRACT This paper aims to evaluate the potential of a natural Algerian pozzolan for use in cement-based materials. This pozzolan can be classified in the group of pyroclastic rocks, like the Italian pozzolan, and that it respected the specifications for natural pozzolans as given in American (ASTM C618), Canadian (A3001), French (NF P 18–308) and Algerian (NA 2830) standards. The effects of the pozzolan on the fresh state of mortars showed that it led to an increase in water demand and a slight increase in setting time. For hardened mortars, the long-term strengths were higher for replacement rates of up to 30%, without increasing the free shrinkage of prisms. These results appear to show that it is possible to obtain cement-based materials having correct properties by using only 70% of cement, thus confirming the interest of this kind of material, especially in developing countries.

Technological and environmental behavior of sewage sludge ash (SSA) in cement-based materials

Sewage sludge ash (SSA) is a waste material obtained from the incineration of wastewater sludge. The physical, chemical and mineralogical characteristics of SSA, and the evaluation of its use in cement-based materials, are presented in this paper. Results show that SSA is composed of irregular grains having a high specific surface area and thus leading to a significantly high water demand. A fraction of the ash is rapidly soluble (sulfates, aluminum and silica) and can create new-formed products in presence of lime. SSA induces short delays of cement hydration, probably due to both minor elements of the ash and dilution effect. Compressive strengths of mortars containing 25% and 50% of SSA are always lower than those of reference mortars but it is shown that SSA has a long-term positive effect which might be related to a slight pozzolanic activity. The amount of elements leached from SSA mortars is slightly higher than from the reference mortar without residue but it remains of the same order of magnitude. An extensive literature review was performed in order to compare the residue used in this study with others included in the same category. This analysis highlighted the principal characteristics that must be taken into account to use SSA correctly in cement-based materials.

Use of sewage sludge ash as mineral admixture in mortars

This paper presents the physical, chemical and mechanical characteristics of sewage sludge ash (SSA), in order to compare its properties with the standard requirements for coal fly ash (FA). It also provides an evaluation of its environmental behaviour when used as a mineral admixture in cement-based materials. Results show that, compared with FA, SSA has a high amount of calcium and phosphorus but a relatively low fraction of silica. SSA is composed of irregular grains having a high specific surface area and thus leading to a high water demand. The high water absorption of SSA requires an increase of the water–binder ratio of mortars, or the use of a water-reducing admixture. The strength activity index (25% replacement of cement) reaches more than 90% after 28 days, showing a long-term positive effect, which might be related to the pozzolanic activity. The amount of leached elements of SSA mortars is slightly higher than for the reference mortar without residue, but it remains within the same order of magnitude. The comparison of the characteristics of SSA with the FA specifications given by American and European standards shows that SSA does not satisfy the requirements to be directly considered as a mineral admixture. Nevertheless, these preliminary results show that SSA could be classified between filler and pozzolanic admixtures. Thus SSA may not necessarily be excluded from use in cement-based materials.

Corrosion inhibitors in concrete: Part III. Effect on time to chloride-induced corrosion initiation and subsequent corrosion rates of steel in mortar

The effectiveness of four commercially available corrosion inhibitors for use in cement-based materials was assessed in mortar exposed to chloride solution. Although, in a parallel study of steel in synthetic pore solutions, the inhibitors were observed to be ineffective in increasing the chloride threshold value of reinforcing steel exposed to chlorides, in the present study all inhibitors were found to delay the onset of corrosion, but to differing degrees. Moreover, in agreement with the parallel study, the inhibitors were found to have little detectable effect on the corrosion rate of the embedded steel once active corrosion had been initiated. This study confirmed that calcium nitrite inhibitors delay the onset of corrosion but raises questions regarding the mechanism of inhibition.

Titanium fume and ilmenite fines characterization for their use in cement-based materials

A series of characterization experiments was conducted to evaluate two by-products from the iron and titanium industry (ilmenite fines and titanium fume) to be use in cement-based materials. Although these by-products show a weak reactivity (early age), their physical properties, especially in the case of titanium fume, which is formed of spherical particles with a mean particle diameter of 1.7 μm, lead to an enhancement of the mechanical strength of mortars (for mortars containing up to 5% replacement of cement). For larger substitution rates, their efficiency coefficients stand between those of inert and pozzolanic materials.

Corrosion inhibitors in concrete Part II: Effect on chloride threshold values for corrosion of steel in synthetic pore solutions

The effectiveness of four commercially available corrosion inhibitors for use in cement-based materials was assessed in synthetic concrete pore solution containing chlorides. The effect of the surface topography of the sample and the composition of the pore solution was also assessed. Although in a parallel study the inhibitors were observed to delay the onset of corrosion, in these tests in pore solution they were found to be ineffective in increasing the chloride threshold value of reinforcing steel exposed to chlorides and had little influence on the progression of corrosion once initiated. This suggests that chemical reactions within the cement phase are responsible for the observed results. Metallographically polished samples proved the most resistant to corrosion regardless of electrolyte composition and samples with all surface finishes exhibited lower resistance in solutions containing only calcium hydroxide than in the higher pH synthetic concrete pore solutions.