Durability Of Cementitious Materials Research Articles

A Review on the Application of Nanocellulose in Cementitious Materials.

The development of the concrete industry is always accompanied by some environmental issues such as global warming and energy consumption. Under this circumstance, the application of nanocellulose in cementitious materials is attracting more and more attention in recent years not only because of its renewability and sustainability but also because of its unique properties. To trace the research progress and provide some guidance for future research, the application of nanocellulose to cementitious materials is reviewed. Specifically, the effects of cellulose nanocrystal (CNC), cellulose nanofibril (CNF), bacterial cellulose (BC), and cellulose filament (CF) on the physical and fresh properties, hydration, mechanical properties, microstructure, rheology, shrinkage, and durability of cementitious materials are summarized. It can be seen that the type, dosage, and dispersion of nanocellulose, and even the cementitious matrix type can lead to different results. Moreover, in this review, some unexplored topics are highlighted and remain to be further studied. Lastly, the major challenge of nanocellulose dispersion, related to the effectiveness of nanocellulose in cementitious materials, is examined in detail.

Effects of pH on the nano/micro structure of calcium silicate hydrate (C-S-H) under sulfate attack

Calcium silicate hydrate (C-S-H), the most important Portland cement hydration product, determines the mechanical properties and durability of cementitious materials. In marine environment, C-S-H often suffers from sulfate attack – one of the most common and severe degradations for concrete. pH is considered as a critical factor in determining the deterioration behavior of C-S-H during sulfate attack, of which the significance may be overlooked. This study focused on the role of pH on the deterioration of C-S-H in terms of the composition and nano/micro structure under sulfate attack. The results show that lowering pH aggravates the decalcification of C-S-H, whereas a strong alkaline condition is beneficial to increase the resistance to deterioration. An increase in the mean chain length together with the proportion of large pores (>10 nm) is observed when C-S-H is subjected to low-pH sulfate attack (pH = 10–12), resulting in a relatively loose structure. The deep analysis on defective tobermorite model reveals that calcium at the interlayer of C-S-H nanostructure is readily removed under sulfate attack, thereby improving the potential of Si-O-Si groups formation and increases the mean chain length of C-S-H.

Advances of graphene- and graphene oxide-modified cementitious materials

Abstract Emerging nanomaterials provide an invaluable opportunity for the development of cementitious materials. Many scholars have explored the influence of graphene (GP) and graphene oxide (GO) on the performance of the cementitious materials. This article reviews the previous research on the effect of GP and GO on the properties of cementitious materials. Detailed review of the mechanical properties and durability of cementitious materials containing GP or GO nanofilms is presented, and the mechanism is discussed. The mechanical properties of GO-cementitious materials are significantly enhanced. The optimal improvement of GO-modified compressive, flexural, and tensile strengths is 77.3%, 78.3%, and 78.6%, respectively. The durability of GO- and GP-modified cementitious material is compared with the control group. The incorporation of GP or GO significantly improves the sulfate attack resistance, and the transport properties can be decreased, while the frost resistance of GO- and GP-modified cementitious materials needs further research. This literature review shows that the microstructure of GO- and GP-modified cementitious material is improved in three aspects: accelerating the cement hydration, refining the pore structure, and hindering the crack propagation.

Investigation on parameters optimization for gas permeability testing of concrete: Inlet-gas pressure and confining pressure

Permeability is an important characteristic associated with the durability of cementitious materials. Gas permeability testing could overcome some shortcomings of traditional methods but its key parameters have so far not been identified for long periods, reducing comparability of test results. In this study, coarse-aggregate settlement in concrete was taken into consideration by dividing concrete cores into smaller segments and the gas-permeability of concrete specimens was measured by the modified CemBureau method. Apparent gas-permeability (Ka) values of the segments were determined under multiple inlet-gas pressures (1.0 bar–40.0 bar) and various confining-pressures (30 bar–90 bar), which then were applied to calculate the intrinsic permeability (Kint) values and Klinkenberg coefficient (βk) to obtain optimal parameters of inlet-gas pressure and confining-pressure. Meanwhile, X-ray computed tomography (X-ray CT), mercury intrusion porosimetry method (MIP) and specific gravity method (SG) were used for auxiliary calibration of test parameters. The results showed that four zones with different inlet-gas pressures were observed for apparent gas-permeability: unstable zone, metastable zone, stable zone, and anamorphic zone. Combined with gas-permeability, pore characteristics were employed for auxiliary calibration of parameter optimization. In sum, 15.0 bar–30.0 bar inlet-gas pressure and 50 bar confining-pressure were determined as the best parameters for concrete gas-permeability testing.

Synthesis of silica nanoparticles to enhance the fire resistance of cement mortars

Silica nanoparticles are known to enhance the strength and durability of cementitious materials, due to their nanofilling effect and their high pozzolanic reactivity. They also have the potential to improve their thermal properties and fire resistance. However, these improvements are highly dependent on the nanoparticles’ characteristics. In this work, silica nanoparticles were prepared by sol-gel reaction and a design of experiments with four factors was used to conclude about the parameters that have more influence in the synthesis of these nanoparticles and, thus, optimize this process and the particles’ properties. Using a lower ethanol/water, higher hydrolysis and condensation time and higher volume of catalyst, the smallest particle size was obtained (118 nm). The effect of the incorporation of these silica nanoparticles into cement mortars was studied in terms of density and thermal conductivity of these mortars, after curing at room temperature. The presence of silica nanoparticles led to an increase in density and decrease of thermal conductivity. The mortars were also exposed to high temperature, which originated a significant reduction (~50%) in their thermal conductivity.

A new test for combined Ca-leaching and sulphate resistance of cementitious materials

Limitations in the understanding of chemical key controls on concrete damaging mechanisms exacerbate predictions on the long-term performance and durability of cementitious materials. Therefore, the scope of the project “ASSpC Advanced and Sustainable Sprayed Concrete” is to obtain a better mechanistic understanding of the processes underlying deleterious chemical attacks. The herein presented alternative test, loosely following the regulations of the German Building Authority (DIBt) testing procedure (the so-called SVA test) for sulphate resistance, investigates the resistance of concrete mixes with high levels of limestone substitution (35%, 50% and 65%) against sulphate attack in a 10 g L-1 Na2SO4 solution at ambient temperature. Powdered samples were used in favour of prisms or drill cores to accelerate alteration reactions and to eliminate variations in microstructure or porosity. Based on throughout chemical and mineralogical characterisation of the experimental solutions and solid materials, we identified and traced several mineral reactions taking place in a chronological order: (1) dissolution of portlandite and Ca-leaching from C-S-H started immediately at the beginning of the experiments and provided the physicochemical conditions favourable for (2) the precipitation of massive calcite and ettringite during the advanced stage of chemical attack. Ongoing changes in the aqueous composition indicate that C-S-H dissolves incongruently and may be transformed into Si-bearing hydrogarnet. The amount of precipitated ettringite is apparently controlled by the availability of calcium, sulphate and aluminium and the precipitation rate correlates with the superplasticiser demand of the concrete mixes and with the pH of the solution during the nucleation and crystal growth stages, respectively. Our test allows distinguishing between competing reaction paths and kinetics and is capable to provide new insights into concrete damaging mechanisms in sulphate-loaded aqueous environments.

Assessment of the effect of nanosilica on the mechanical performance and durability of cementitious materials

Over the last years, nanotechnology is getting more attractive and nanomaterials are being used more commonly in construction industry. One of these materials is nanosilica: the nano-sized, engineered form of silica fume. The replacement of cement by these nanoparticles is said to enhance both the mechanical performance and the durability of the concrete material. In this paper colloidal silica will be used, which is nanosilica in solution. A characterization of mortar mixtures containing different amounts of silica is done and a comparison is made with respect to a reference mixture.

Bioprecipitation of calcium carbonate induced by Bacillus subtilis isolated in Brazil

In view of the growing concern about improving the characteristics and durability of cementitious materials, additions of bacteria, mainly of the genus Bacillus, are being studied as pore and crack filling through calcium carbonate precipitation (CaCO3). In this sense, the present study tested the strain B. subtilis AP91, isolated from rice leaves of the early Agulha variety, in the precipitation of CaCO3 by means of the change of pH during the formation of biofilm, in order to verify the potential of use of this bacterium to close pores and cracks in cementitious materials. To this end, the strain B. subtilis AP91 was inoculated in the B4 precipitation medium. The analysis of bacterial biofilm production and the evaluation of the morphology of precipitated crystals were performed using a Scanning Electron Microscope (SEM) and CaCO3 was quantified by the difference of mass retained on the filter with 2 μm micropores. The results showed that the bacterium B. subtilis AP91 has high capacity for CaCO3 precipitation, and may have advantageous applications in the closure of pores and cracks in cementitious materials.

Application on cementitious materials to promote durability of alkali-activated concrete containing co-fired fly ash and water-quenched slag

In the present study, we evaluated the effects of using co-fired fly ash (waste product of paper making) and water-quenched slag (waste product of iron smelting) in the manufacture of cementitious materials (CM). Rapid chloride permeability results revealed that less charge passes through CM than through ordinary Portland cement (OPC), indicating the superior durability of CM. However, the results of water permeability testing led to the opposite conclusion. Absorption capacity results revealed that the durability of CM is lower than that of OPC. Previous studies have shown that the strength of CM is only 70% that of OPC. This is a clear indication that CM containing co-fired fly ash and slag should not be used for primary structures, i.e., its use should be limited to secondary structures such as bricks or PC-based materials.

Intermolecular Forces between Nanolayers of Crystalline Calcium-Silicate-Hydrates in Aqueous Medium

Calcium-silicate-hydrate (C–S–H) is the major binding phase responsible for strength and durability of cementitious materials. The cohesive properties of C–S–H are directly related to the intermolecular forces between its layers at the nanoscale. Here, we employ free energy perturbation theory (FEP) to calculate intermolecular forces between crystalline C–S–H layers solvated in aqueous medium along face-to-face (FTF) and sliding reaction coordinates. Contrary to mean-field theories, we find that our counterion-only system exhibits an oscillatory behavior in FTF interaction. We correlate these oscillations with the characteristic length scale comparable to the distance between interfacial water layers at the hydrophilic surface of crystalline C–S–H. We attribute the sliding intermolecular forces to the atomic level roughness of crystalline C–S–H layers stemming from the local arrangement of nanoscale structural motifs. These intermolecular forces provide a direct access to the key mechanical properties, su...

Latex influence on the mechanical behavior and durability of cementitious materials

The results of an experimental program conducted on latex-modified mortars are presented in this article. These mortars have become of growing interest in the field of construction. They were used as superplasticizers, or water reducers, for finishing work applications and for repairs, coatings, and waterproofing. This study is about using two polymers (latex), i.e. styrene–butadiene rubber and styrene–acrylic, in order to assess their performance in replacing cement in mortars. A series of mortar mixtures, containing 0, 2.5, 5, 10, 15, and 20% of solid polymer latex (by weight), were prepared and tested in the fresh and hardened states. The test parameters include the fluidity, compressive and flexural strengths, porosity accessible to water, adhesion to clay bricks, and cementitious substrates. The experimental results showed that substituting cement into modified mortars improves their fluidity and adhesion. In the case of clay substrates, a cohesive failure occurs within the substrate layer beyond 10% of substitution, while the rupture takes place at the interface for all formulations tested on cementitious substrates. It was also noted that the flexural tensile strength improved beyond 60 days. However, the compressive strength of polymer mortars decreased with the substitution rate of cement, for all maturities considered. However, for porosity accessible to water, the results follow a linear function, with an inflection at 5% of latex substitution.

Reuse Research Progress on Waste Clay Brick

Waste clay brick (WCB) is silicate solid waste, its recycling has great environmental and social significance. The application of WCB as recyclable coarce and fine aggregate in concrete and mortar, wall materials, as well as raw material or addition in the production of recyclable cement, has been briefly introduced. The following aspects were emphasized: the research progress of the impact of WCB as supplementary cementitious material on physical mechanics, deformation and durability of cementitious materials; the progress of the function of WCB as environmental materials on eliminating fluorine, ammonia nitrogen and phosphate in waste water; the current research status of the impact of WCB as recyclable aggregate on the mechanics, durability of GRC; the current status of WCB as filler in decorative paints, as filler in rubber plastic materials after being organically modified, as well as in the production of recyclable ancient architectural brick in recent years. The problems in recycling of WCB has also been summarized.

Mechanical properties and durability of self consolidating cementitious materials incorporating nano silica and silica fume

In recent years, the emergence of nanotechnology and nanomaterial has created hopes to improve various properties of concrete. Nano silica as one of these materials has been introduced as a cement replacement material for concrete mixture in construction applications. It can modify the properties of concrete, due to high pozzolanic reactions and also making a denser microstructure. On the other hand, it is well recognized that the use of mineral admixtures such as silica fume affects the mechanical properties and durability of cementitious materials. In addition, the superior performance of self-consolidating concrete (SCC) and self-consolidating mortars (SCM) over conventional concrete is generally related to their ingredients. This study investigates the effect of nano silica and silica fume on the compressive strength and chloride permeability of self-consolidating mortars. Tests include compressive strength, rapid chloride permeability test, water permeability, capillary water absorption, and surface electrical resistance, which carried out on twenty mortar mixtures containing zero to 6 percent of nano silica and silica fume. Results show that SCMs incorporating nano silica had higher compressive strength at various ages. In addition, results show that nano silica has enhanced the durability SCMs and reduced the chloride permeability.

Durability of Photocatalytic Cement after Nitric Oxide-Wet-Dry Cycling

Photocatalytic cement has been receiving attention due to its high oxidation power that reduces nitrogen oxide, thus contributing to a clean atmospheric environment. However, there has not yet been a thorough investigation on the effect of photocatalytic reactions on the durability of cementitious material, the parent material. In this study, photocatalytic cement samples were exposed to nitric oxide gas and UV along with cycles of wetting and drying to simulate environmental conditions. The surface of samples was characterized mechanically, chemically, and visually during the cycling. The results indicate that that the photocatalytic efficiency decreased with continued NO oxidation. The pits found from SEM indicated that chemical deterioration, such as acid attack or leaching, did occur. However, this was not confirmed by X-ray diffraction. The hardness was not affected, probably due to the formation of CSH as evidenced by the XRD pattern. In conclusion, it was found that photocatalysis could alter cementitious materials both chemically and mechanically, which could further affect long-term durability.

Microstructure and permeability of concrete with glass powder addition conserved in the sulphatic environment

Most mechanical properties and durability of cementitious materials are related to the performance of the hydrated cement that coats the granular skeleton. In this paper, concrete is formulated by substituting 30% of cement by finely ground glass powder. The experimental study consists of investigating the effect of conservation in tap water or sulphate water on the performance of concrete. The mechanisms of concrete damage have been related to the development of the microstructure of the material. The degradations were observed using scanning electron microscope (SEM) and quantified by X-ray diffraction (XRD). In addition, chloride ions permeability and gas permeability tests were performed. The results showed that glass powder presents a pozzolanic activity and hence it affects favourably the microstructure of the paste which becomes denser and less permeable.

Impact of carbonation on the durability of cementitious materials: water transport properties characterization

Within the context of long-lived intermediate level radioactive waste geological disposal, reinforced concrete would be used. In service life conditions, the concrete structures would be subjected to drying and carbonation. Carbonation relates to the reaction between carbon dioxide (CO2) and the main hydrates of the cement paste (portlandite and C-S-H). Beyond the fall of the pore solution pH, indicative of steel depassivation, carbonation induces mineralogical and microstructural changes (due to portlandite and C-S-H dissolution and calcium carbonate precipitation). This results in the modification of the transport properties, which can impact the structure durability. Because concrete durability depends on water transport, this study focuses on the influence of carbonation on water transport properties. In fact, the transport properties of sound materials are known but they still remain to be assessed for carbonated ones. An experimental program has been designed to investigate the transport properties in carbonated materials. Four hardened cement pastes, differing in mineralogy, are carbonated in an accelerated carbonation device (in controlled environmental conditions) at CO2 partial pressure of about 3%. Once fully carbonated, all the data needed to describe water transport, using a simplified approach, will be evaluated.

Methodological Approaches to 3D Pore Structure Exploration in Cementitious Materials

About 6% of global CO2 emissions are due to cement production. Blending of Portland cement with a significant fraction of mineral admixture could therefore be instrumental in reducing such emissions. Use of an admixture of vegetable origin such as rice husk as will additionally contribute to waste management and its incineration produces energy. This paper will stress the importance of properly designing such blends. Preferably gap-graded concepts should be employed, since blending efficiency in terms of strength development is promoted as shown in earlier publications. The paper therefore only briefly covers these aspects. Assessment of this blending concept on durability of cementitious materials constitutes a far more complicated problem. This requires careful porosimetry. Mostly, this problem is approached by MIP or by quantitative image analysis. Both can provide 3D information, although that of MIP is generally significantly biased. Quantitative image analysis is however time-consuming and laborious, and thus expensive. Moreover, it does not provide information on continuity of pores. Present day computer facilities offer therefore a better alternative. When using a proper DEM system, the concrete can be simulated in a realistic way. The paper describes new methods for investigating the pore structure in virtual concrete and presents some data on pure cement and blended cement. Differences will have impact on durability risks.

Effect of rice-husk ash on durability of cementitious materials

Abstract In this paper the effects of partial replacements of Portland cement by rice-husk ash (RHA) on the durability of conventional and high performance cementitious materials are investigated. Different percentages of RHA replacement levels, two RHAs (amorphous and partially crystalline optimized by dry-milling) and several water–cementitious materials ratio are studied. The following durability aspects were tested: air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance. The results were compared with those of cementitious materials without RHA. It is concluded from the tested properties that the incorporation of both RHAs in concretes show different behaviors for air permeability and chloride ion penetration depending on the water/cementitious materials ratio used; in mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction. The results of durability aspects due to physical or pozzolanic effects after the addition of both RHAs, and its chemical composition, in general indicate an enhanced performance, proving the feasibility of its rational utilization as a supplementary cementing material.

High durability cementitious material with mineral admixtures and carbonation curing

Nuclear waste repositories need highly durable cementitious materials to function for over thousands of years while resisting leaching and degradation. The durability of cementitious material can be effectively improved by reducing permeability and by changing cement hydrates to a less soluble matrix. This paper describes the properties of carbonated new cementitious materials containing belite-rich cement and γ-2CaO · SiO 2 as main components. In addition, the long-term leaching properties are investigated and compared with ordinary Portland cement by using a predictive leaching model.

The deterioration of mortar in sulphate environments

The skin of concrete plays an important role in the durability of cementitious materials. In a sulphate environment this surface reaction can cause deterioration or in some cases protection. Surface properties of mortars, which are exposed to sulphate environments, have been studied using SEM, microanalysis, X-ray diffraction and Vickers’ hardness testing. When cement mortar is exposed to sulphuric acid a dense layer of gypsum is formed; this is capable of retarding the deterioration process by acting as a surface sealing layer. Gypsum also exists in pores and fissures in the surface zone, indicating that the attack is due to expansive crystallisation. In ammonium sulphate the surface deposit of gypsum is sparse and the damage to the concrete occurs to a greater depth. The lack of sulphur found in the surface zone indicates that the mechanism of deterioration is due to the dissolution of Ca 2+.