Surface Of Cementitious Materials Research Articles

Rapid carbonate precipitation induced by carbamate coating: A new approach to form impermeable thin barrier and its mechanism

Various coating strategies have been explored in the past to prevent the ingress of aggressive substances into concrete. However, either the durability or performance is still far from satisfaction. Here, carbamate solutions were prepared by pre-absorbing CO2 into amino acid salts (AASs) to carbonize the surface of cementitious materials. The high concentration of carbonate ions provided by the carbamate induced rapid surface carbonation, resulting in the formation of an AAS-CaCO3 composite barrier with a thickness of 2–3 μm and possessing high micromechanical properties. Additionally, it was observed that the barrier's effectiveness depends on the molecular structures of the amino acids employed. Coatings formed by arginine-based carbamates demonstrated excellent performances, likely due to the highly compacted calcite particles they produced. This easy-to-operate and effective strategy has the potential to open new avenues for the development of highly durable and impermeable coating barriers for practical applications.

Research on the bonding behavior and durability of cement-asphalt mortar acted as repair and protective layer

In order to enhance the durability of cementitious materials, cement-asphalt mortar (hereafter shorted as CA mortar) acted as a coverage of protective layer on the surface of cementitious materials was employed to block the migration of water and ions in this investigation. The results demonstrated that the ratio of flexural strength to compressive strength increased as the increase of asphalt emulsion to cement ratio (A/C), while the fracture energy of CA mortar arrived a peak value at the A/C of 0.15, corresponding to the optimal toughness of CA mortar of 83.16 J/m2. The bonding strength between CA mortar and substrate mortar decreased gradually from 1.55 MPa to 1.26 MPa as the increase of A/C from 0 to 0.45, which could still satisfy the requirement of repair and protective mortar. The electrical flux of CA mortars with A/C of 0.15, 0.3 and 0.45 decreased by 21.47 %, 26.68 % and 27.59 % in relative to the CA mortar with A/C of 0. As the rising of A/C, the resistance capacity of CA mortar on the sulfuric acid (pH=1) corrosion improved significantly. All in all, the durability of CA mortar under the chloride and acid environments was improved considerably as the A/C increasing. However, the frost resistance of CA mortars deteriorated gradually with the increase of A/C from 0 to 0.45 after the freeze-thaw cycles, that is, the application of CA mortars should be avoided in the cold condition.

Effect of clay fraction on the mechanical properties and microstructural characteristics of waste rock fine-based brick

The disposal of waste rock fine (WRF) from the manufacturing process of crushed aggregates is attracting more and more attention due to the thorny issues related to clay particles. This paper investigated the use of WRF as a substitute for fine aggregate that solidified by phosphogypsum (PG), groundgranulated blast-furnace slag (GGBS), and ordinary Portland cement (OPC) system in manufacturing of baking-free brick. Three kinds of WRF with different clay fraction (i.e., natural WRF, silty WRF, and clayey WRF) were prepared via slurry settlement methods. Thereafter, their mechanical behaviors were compared by unconfined compressive strength (UCS), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests. The results show that natural WRF contains 81.9% silt and 18.1% clay, after settling-based separation process, the strength of solidified silty and clayey WRF samples decreased by 4.1% and 16.5% at 28 days curing period. Micromorphology, compositional, and microstructural analyses indicate that the strength of solidified WRF is governed by both bonding and filling effect, therein, the strength of solidified silty and clayey WRF samples were lower as compared with natural WRF-based modified samples due to the gradation effect. In addition, it was noticed that although clay particles may participate in the secondary pozzolanic reaction to contribute bonding strength, they also possess superior adsorption capability owing to the large specific surface area, which will adsorb on the surface of cementitious materials and thus hinder the hydration reaction. Moreover, water stability, environmental leaching, economic, and greenhouse gas emission results further confirmed the advantage of reusing WRF and industrial by product resources.

A study on the interactions between polycarboxylate ether superplasticizer and montmorillonite

The adsorption of polycarboxylate ether (PCE) superplasticizer on the surface of cementitious materials is a prerequisite for its dispersion and water reduction capability. This paper investigated the adsorption isotherms and kinetics of PCE on montmorillonite (MMT) at 278, 288, 298, and 308 K, respectively. Based on the adsorption behaviors, the critical intercalation concentration of PCE was estimated, and the characterizations of surface adsorption and intercalation were examined. Results show that when its concentration is <0.9 mg/mL, PCE is mainly adsorbed on the surface of MMT. The galleries of MMT are intercalated by the side chain of PCE completely at a concentration of 10 mg/mL. The adsorption isotherms and kinetics of PCE on MMT follow the Freundlich isotherm equation and the pseudo-second-order adsorption equation, respectively. The surface adsorption of PCE is not affected by the temperature, but it presents a lower adsorption saturation at a higher temperature. PCE shows a monolayer thickness of 5.63 nm on the surface, but intercalation conforms to multi-layer adsorption.

Self-Healing of Cementitious Materials via Bacteria: A Theoretical Study

Cracks on the surface of cementitious composites represent an entrance gate for harmful substances—particularly water—to devastate the bulk of material, which results in lower durability. Autogenous crack-sealing is a significantly limited mechanism due to a combination of the hydration process and calcite nucleation, and self-healing cementitious composites are a research area that require a great deal of scientific effort. In contrast to time-consuming experiments (e.g., only the preparation of an applicable bare concrete sample itself requires more than 28 days), appropriately selected mathematical models may assist in the deeper understanding of self-healing processes via bacteria. This paper presents theoretically oriented research dealing with the application of specific bacteria (B. pseudofirmus) capable of transforming available nutrients into calcite, allowing for the cracks on the surfaces of cementitious materials to be repaired. One of the principal objectives of this study is to analyze the sensitivity of the bacterial growth curves to the system parameters within the context of the logistic model in the Monod approach. Analytically calculated growth curves for various parameters (initial inoculation concentration, initial nutrition content, and metabolic activity of bacteria) are compared with experimental data. The proposed methodology may also be applied to analyze the growth of microorganisms of nonbacterial origin (e.g., molds, yeasts).

Formation mechanism and microhardness characterization of the ultrasonic hardening layer in cementitious materials

AbstractUltrasonic surface treatment (UST) is a novel treatment method to improve the durability of cementitious materials, resulting in the formation of an ultrasonic hardening layer (UHL). The UHL acts as an effective natural coating, offering penetration and erosion protection. However, the formation mechanism and the quantitative characterization of the UHL have not been studied, and the validity of the UST on the top and side surfaces of cementitious materials is still unknown. Therefore, in this study, we investigated and proposed a formation mechanism for the UHL, and defined a transition layer between the UHL and the matrix. We also utilized HV microhardness testing to provide an effective quantitative characterization method for the UHL. Finally, using a set of custom‐designed ultrasonic molds, we confirmed the validity of the UST on the top and side surfaces of the cementitious materials.

Cerium oxide nano-particles application for self-cleaning building material

Photocatalytic degradation has gained attraction in the self-cleaning construction materials applications because of its ability to be used to protect surface of cementitious materials and minimize the negative effects of environmental conditions on building, and to remove the dyes and other organic pollutants from water and wastewater. In this study, the influence of nano-Ceria particles on the photocatalytic degradation of methylene blue dye of cement mortar samples was investigated. In this work, nanoceria was prepared via simple co-precipitation method. Nanoceria is a powerful photocatalyst due to its high visible-light absorptivity, strong redox ability, high oxygen storage/release capacity, eco-friendly nature, photostability and cost effectiveness. Nano ceria showed a photocatalytic and self-cleaning activity in the presence of sun radiation. Nano ceria particles were characterized by X-ray diffraction, High resolution transmission electron microscope, and Ultra-violet visible spectroscopy. The presence of active oxygen species detected on nano- ceria surface was identified as cause of the photobleaching of dyes in presence of UV-irradiated.

Biodeterioration kinetics and microbial community organization on surface of cementitious materials exposed to anaerobic digestion conditions

Anaerobic digestion is a process that can produce renewable energy through the fermentation of biodegradable biomass. Industrial anaerobic digestion tanks are usually made of concrete but the production of various aggressive compounds (CO2, NH4+ and volatile fatty acids) during the microbial fermentation leads to deterioration of the concrete structure. In addition, the formation of a microbial biofilm on the cementitious material surface could generate even more intense biodeterioration. The objective of this study is to gain a better understanding of the involvement of biofilm in the biodeterioration of cementitious materials during an anaerobic digestion process. More specifically, the study focuses on the heterogeneity of microbial populations within the biofilm and the reactive medium in anaerobic digestion. Laboratory scale anaerobic bioreactors mimicking the industrial anaerobic digestion medium were constructed and CEM I cement pastes were immersed in this medium for 2, 3, 4, 5, 10 and 15 weeks. The biodeterioration of the cement pastes was evaluated by determining the deteriorated thickness. The aggressive compounds in the medium were quantified. The biofilm attached to the surface of the cement pastes was analyzed using 16 s rRNA gene sequencing. To evaluate the heterogeneity of the biofilm, the growth of biofilm layers was successively caused to stall by using two distinct biofilm removal techniques. Three microbial fractions were defined: planktonic microorganisms, and the microorganisms within the biofilm that were loosely and strongly attached. The results showed that the planktonic lifestyle was more associated with microorganisms producing methane and consuming volatile fatty acids, while the biofilm was more associated with bacteria producing acids, mainly members of the Clostridium genus. A microbial community shift due to a reversible propionic acid accumulation during the first 5 weeks was also observed. In addition, no major differences were spotted between the loosely and strongly attached biomass, indicating homogeneity in the two layers of the biofilm. These results suggest that the biofilm could increase the biodeterioration of concrete since volatile fatty acids could be produced in massive quantities near the surface of the cement samples by the acidogenic microbial population more present within the biofilm.

Ultrasonic surface treatment for improving wind-blown sand erosion resistance of cementitious materials

In this study, we present a method that employed ultrasound to impose vibration on the surfaces of cementitious materials at the early stage of hydration to form a hardening layer and improve the surface hardness. The formation mechanism of the ultrasonic hardening layer (UHL) was analyzed, and the density and surface hardness of the UHL were measured. An experimental study was carried out to determine the effect of the UHL on improving the wind-blown sand erosion resistance of cementitious materials. Experimental data show that the UHL has a density 3.3% greater and a hardness 136% greater than that of the contrast samples after 28-days of curing. Wind-blown sand erosion tests data show that to the specimens with 28-days curing age, the UHL can improve the erosion resistance for 12.8–24.1% versus that of the contrast in a 30-min erosion procedure. • A layer known as the UHL can be formed by ultrasonic vibration applied on the surface of cementitious composites. • UHL had the characteristics of higher density and higher surface hardness. • In the UHL, the micro-structure of the composite was promoted. • The UHL improved the erosion resistance of the cement mortar specimens in a wind-blown sand erosion test.

Effects and mechanisms of surface-treatment of cementitious materials with nanoSiO2@PCE core-shell nanoparticles

A commercial interest in the improvement of durability is driving efforts to develop new generation of surface-treatment agents. In the previous paper, a series of nanoSiO2-polycarboxylate superplasticizer core-shell nanoparticles (NS@PCE) were synthesized by “grafting to” method. In this paper, we aim to explore the potential of NS@PCE to densify the surface of cementitious materials, and to study the mechanism of nanoparticles surface-treatment process by measuring water absorption ratio, dispersion stability, pozzolanic reactivity, and mercury intrusion porosimetry. Results show that NS@PCE is effective in reducing the water absorption. Various NS@PCE present different influences, it seems that NS@PCE with a moderate shell-core ratio is a more reasonable choice. A hypothesis was proposed to explain the surface-treatment effect of nanoparticles, it utilizes two properties (dispersity and pozzolanic reactivity) of nanoparticles to describe their refining-pore performance. This research indicates a new pathway for nanoSiO2 to optimizing cementitious materials.

Preparation, Physicochemical Properties, and Long-Term Performance of Photocatalytic Ceramsite Sand in Cementitious Materials

Incorporation of TiO2 into cementitious materials is an important technology in the field of photocatalytic pollution mitigation; however, the photocatalytic activity of TiO2 is limited by specific surface area, poor gas diffusion and light transmission performance of cementitious materials. In this study, a novel photocatalytic lightweight aggregate—photocatalytic ceramsite sand (PCS) was synthesized by loading TiO2 on activated porous ceramsite sand (CS) with negative pressure method to solve problems in application of photocatalysts in cementitious materials. Photocatalytic cement material (PCM) was prepared by loading PCS on the surface of cementitious materials, which improved the photocatalytic activity and efficiency of TiO2 in cementitious materials. It was found that the pore structure (pore volume, size distribution and interconnectivity) of ceramsite sand (CS) varies with particle size. The photocatalytic removal rate of benzene on PCS increased significantly through adjusting ceramsite sands in appropriate pore structure and TiO2 at best coating ratio. The photocatalytic activity of PCS slightly decreased but still remained active after incorporated into concrete. 2 μL benzene was degraded completely in 200 min by 5 g 4PCS-1.25~2.35 and 300 min by PCM-5, and was still degraded over 80% in 400 min by PCM-5 after exposure to natural environment for 6 months. The results suggested that the photocatalytic activity of TiO2 in cementitious materials was enhanced by the preparation of PCS and PCM, which could provide more gas diffusion, higher specific surface area, more TiO2 active sites, and prevent TiO2 particles from being influenced by the envelope of cement hydration products and the carbonation of cement.

Durability of superhydrophobic engineered cementitious composites

Key elements of infrastructures throughout the United States are displaying poor durability, especially in northern regions where freeze–thaw damage is prevalent. One main factor leading to the early deterioration of concrete is related to the infiltration of water into the porous structure of the concrete matrix. To account for this, sealers or water repellant coatings are often applied on the surface of cementitious materials to reduce the ingress of water into the material. However, when the material develops micro-cracks, which is unavoidable, water can easily penetrate and saturate the bulk of the material. By incorporating a hydrophobic admixture within the concrete mix, water is restricted to enter the capillary voids and porous space, where, upon freezing, damage occurs. This type of modification is achieved in superhydrophobic engineered cementitious composites (SECC) designed with hydrophobic or superhydrophobic air voids evenly distributed throughout the cementitious matrix, providing effective protection against water infiltration. Moreover, SECC incorporates fiber reinforcement tuned to limit the crack opening. The reported research demonstrates the improved durability in fiber reinforced cementitious materials by creating a 3-dimensional hydrophobization to reduce the water absorption and permeability as well as to improve the freeze–thaw performance.

Influence of electrified surface of cementitious materials on structure formation of hardened cement paste

To provide high strength and durability of concrete it is necessary to study the influence of physical and chemical and mechanical principles of dispersed cementitious systems. The experimental bench was developed to study the influence of electrified surface of cementitious materials on structure formation of hardened cement paste. The test bench allows accelerating the processes of dissolution of cementing materials in water due to influence of electric discharge on their surface. Cement activation with high-voltage corona discharge when AC current is applied allows increasing the ultimate compressive strength of hardened cement paste by 46% at the age of one day and by 20% at the age of 28 days.

Measurement of early-age strains in mortar specimens subjected to cyclic temperature

As well known, the volume change induced by environment temperature variation can lead to cracking at the surface of cementitious materials with low water-cement ratio. Thus, it can be said that there is a pressing need to reveal the early-age performance of cementitous materials in a variable environment temperature. Conventional thermocouple and strain gauge have been widely used for measuring temperature and strain in cementitious materials, respectively. However, conventional sensors have several limitations for measuring strain and temperature in cementitous materials such as too many cables for multipoint measurement, short circuit, and electromagnetic interference. Compared to conventional electrical strain gauge, fiber Bragg grating (FBG) has several inherent advantages including multiplexable, resistance to electromagnetic interference, and stable signal in long distance transmission. In this study, two lines mutiplexed with FBG strain and temperature sensors were fabricated and employed to measure the quasi-distributed strain and temperatures in mortar specimens subjected to cyclic temperature.

Assessment of surface condition of cementitious materials subjected to laser radiation

The paper is focused on the assessment of laser-treated cementitious surfaces. It forms part of the larger study on laser cleaning process and its effect on modifi cation of geometrical microstructure of cementitious composites. The great variation in absorptivity of highly developed surfaces of cementitious materials results in substantial differences in their responses to laser irradiation. Even though lasers can be successfully used to remove dirt from mortar surfaces, there are always some residual surface alterations associated with the removal of mortar, formation of cracks and glazing (melted mortar). Comprehensive understanding of surface processes resulting from laser interaction with substrate is essential in further industrial commercialisation of the technology. In order to address the problem a wide range of laser-treated samples with different internal microstructures, surface roughness and moisture content were studied. The characteristic features of all laser-cleaned areas included removal of mortar, formation of cracks and glassy patches. Systematic analysis of surface modifi cations resulting from laser cleaning confi rmed a strong relationship between initial roughness of surfaces and their end conditions. An increase in initial surface roughness leads to more pronounced alterations in roughness and reduced tendency towards crack formation.

Applying a polyurea coating to high-performance organic cementitious materials

Polyurea is a polymeric material that can be used to provide environmental protection and structural enhancement. In this study, a low modulus polyurea coating, having high elongation and energy absorption capacities and a fast gel time, was sprayed under field conditions onto the surfaces of cementitious materials. Compression tests were conducted to establish the wet–dry performance of uncoated and circumferentially coated cylinders fabricated from a high-performance matrix constructed with Poly(vinyl butyral) (PVB) as the only aggregate. Results showed that the coating increased the compressive strength of specimens exposed to both fresh and sea water environments. Similar results were obtained when a lightweight matrix containing sand was subjected to the same sea water environment. Flexure tests were conducted on uncoated and fully encapsulated plates kept under normal operating conditions to establish the stress–strain behavior of these two matrices, as well as a PVB matrix with Poly(vinyl alcohol) (PVA) fibers added as reinforcement. Results showed that the addition of the fibers and the coating increased the ultimate flexural strength, decreased the stiffness, allowed the structure to sustain higher strains prior to failure, and increased the fracture toughness. Comparisons are made between the performance of lightweight and high-performance concretes.

Full paper: Digital photogrametry in investigation of application membranes on the surfaces of cementitious materials

Full paper: Digital photogrametry in investigation of application membranes on the surfaces of cementitious materials

Digital photogrametry in investigation of application membranes on the surfaces of cementitious materials

Purpose The purpose of this work is to demonstrate usage of the photogrametry in construction, testing and monitoring of structures. Method The method of photogrametry is based on capturing digital shots of the cementitious surface covered with a membrane preventing water loss from concrete either by single shot or time-lapse method. By converting the pictures into gray scale and analyzing the brightness either of the whole surface or any differential area, we are able to calculate an evenness of the membrane application, a prediction of water loss from cementitious material, humidity underneath the membrane, and the areas of the structure most likely weakened due to excessive water loss. Results & Discussion We analyzed the effectiveness of concrete curing by application of a membrane (paraffin–based) on the surface of fresh concrete while studying loss of water depending on boundary conditions of the exposure to the ambient environment. The results in the picture help to refine the data and show this is a means of curing works up to 70%.

AFM study of the interactions between moisture and the surface of cementitious materials

AFM study of the interactions between moisture and the surface of cementitious materials

Discussion: The fractal surface of cementitious materials determined by impedance spectroscopy

Discussion: The fractal surface of cementitious materials determined by impedance spectroscopy