Properties Of Cementitious Composites Research Articles

Elastic properties of cement-based composites reinforced by nano-tailored hybrid fiber

The elastic properties of cementitious composites reinforced by nano-tailored hybrid fibers are analyzed using a micromechanical method. The microstructural feature of the hybrid fiber is that uniformly aligned carbon nanotubes (CNTs) are grown radially on the circumferential surface of carbon fibers (CFs). The CNT waviness and CNT/cement interfacial region are considered. The predictions are compared with experiments, which guarantee the validity of the model. The mechanical properties of cementitious composites, especially in transverse direction, are enhanced due to the radial growth of CNTs on the CFs. The CNT/cement interfacial zone may have a significant effect on the elastic behavior of the nano-tailored hybrid fiber-cement composites. As the mechanical properties of interphase are higher than those of the cement matrix, increasing the interphase thickness causes an improvement in the elastic and shear moduli. The CNT non-straight shape decreases the transverse elastic modulus.

Review on the correlation between mixing, microstructure and strength of cementitious products with nanoparticles

Concrete is manmade multiphase composite where coarse granular materials are embedded in a hard matrix of binder, filling the space between the aggregate particles and gluing them all together that strengthens with time on hydration. Addition of nanoparticles further enhances the properties of the concrete such as early strength, refined micro structure and enhanced durability. Nanoparticles are added to cementitious composites by dry mixing with cement or dispersion in water. The challenge associated with it is the uniform dispersion of the nanoparticles in the matrix of the composite. The type of mixer and the mixing pattern affect the fresh and hardened properties of the concrete. This article reviews the effect of dispersion of nano particles, type of mixer and mixing pattern on the properties of cementitious composites.

Effect of Degree of Hydrolysis of Polyvinyl Alcohol on Adhesive Properties of Cement Mortar

Abstract Polyvinyl alcohol (PVA) is widely used in the building industry to improve the fresh and hardened properties of cement composites. In this article, the effect of partially and fully hydrolyzed PVA on physical and adhesive properties of fresh and hardened cement mortar was investigated. Results showed that both partially and fully hydrolyzed PVA could significantly improve the adhesive properties of cement mortar. The mode of rupture changed from mostly interfacial rupture without PVA in cement mortar to mixed-mode interfacial-cohesive rupture with 1.5 wt.% PVA. Partially hydrolyzed PVA-modified cement mortars had smaller bulk density and higher fluidity compared with fully hydrolyzed PVA. X-ray powder diffraction, thermal analysis, mercury intrusion porosimetry, and scanning electron microscopy were used to investigate cement hydration and microstructure of PVA-modified cement composites. As a result, fully hydrolyzed PVA was more conducive to promote cement hydration and had smaller impact on crystal structure and content of calcium hydroxide (Ca(OH)2) compared with partially hydrolyzed PVA. Besides, the addition of both partially and fully hydrolyzed PVA affected the morphology and the oriented growth of Ca(OH)2 in cement composites. Furthermore, PVA-modified mortar had finer pore size distribution and higher porosity than unmodified mortar.

Synthesis of Highly-Dispersed Graphene Oxide Nanoribbons-Functionalized Carbon Nanotubes-Graphene Oxide (GNFG) Complex and Its Application in Enhancing the Mechanical Properties of Cementitious Composites.

In this study, a graphene oxide nanoribbons–functionalized carbon nanotubes–graphene oxide (GNFG) complex was hydrothermally synthesized as a nanomaterial for reinforcing cementitious composites, using a modified Hummers’ method. Three types of components existed in the GNFG: Type I, the functionalized carbon nanotubes–graphene oxide nanoribbons (FCNTs–GNR); and types II and III are graphene oxide (GO) and functionalized carbon nanotubes (FCNTs), respectively, which exist independently. The dispersivity of GNFG and its effects on the mechanical properties, hydration process, and microstructures of cement pastes were evaluated, and the results were compared with those using cement pastes incorporating other typical carbon nanomaterials. The results demonstrated that dispersion of GNFG in aqueous solutions was superior to that of the CNTs, FCNTs, and GO/FCNTs mixture. Furthermore, the highly-dispersed GNFG (0.05 wt.%) improved the mechanical properties of the cement paste after 28 days of hydration and promoted the hydration of cement compared to CNTs, GO, and GO/FCNTs mixture (0.05 wt.%). The results in this study validated the feasibility of using GNFG with enhanced dispersion as a new nano-reinforcing agent for various cementitious systems.

Investigating the Effect of CNTs on Early Age Hydration and Autogenous Shrinkage of Cement Composite

In this study, the effect of carbon nanotubes (CNTs) on the physical properties of cement composites was investigated. The mechanism of the change of autogenous shrinkage of CNTs-reinforced cement composites was also examined. In the experiments, ordinary Portland cement (OPC) and fly ash (FA) were used as binders, and 0.0, 0.1, 0.3, and 0.5% multi-walled CNTs (MWCNTs) were added to fabricate pastes. When the hydration heat was measured through isothermal calorimetry, it was found that CNTs accelerated the early age hydration of the pastes and that the hydration rate increased as the CNT content increased. The compressive strength was the highest when the CNT content was 0.1%. As the CNT content increased, the internal relative humidity (IRH) decreased and autogenous shrinkage showed a decreasing tendency. Through the analysis of the correlation between autogenous shrinkage and IRH, it was confirmed that the reduction in autogenous shrinkage due to the addition of CNTs resulted from the decrease in bulk strain.

Overview of the influence of waste materials on the thermal conductivity of cementitious composites

The high energy consumption by buildings has called for a need to use energy-efficient material for future construction applications. Cementitious composites in various forms are the most used building material for the construction of buildings. Therefore, in order to ensure these buildings made with cementitious composites are energy-efficient, it is imperative to find innovative and sustainable ways to improve the thermal properties of these cementitious composites. One of the sustainable and effective ways to improve the thermal properties of cementitious composites is with the incorporation of various waste. Therefore, this paper aims to discuss different types of wastes that can be recycled into cementitious composites to improve the thermal properties (i.e. reduce thermal conductivity) based on existing experimental studies. Discussion from this paper showed that recycled materials such as rubber and plastics can be used to reduce the thermal conductivity of cementitious composites when used as a replacement of up to 50% of natural aggregates. It was also concluded that there is a good relationship between density and thermal conductivity of cementitious composites and waste/recycled materials can be incorporated as aggregate/filler in cementitious composites to improve the thermal performance. However, there is a need for the limitations associated with the use of these waste/recycled materials to be resolved before they are incorporated into cementitious composites.

Physics-guided multi-objective mixture optimization for functional cementitious composites containing microencapsulated phase changing materials

A physics-guided multi-objective optimization procedure is developed for the mixture design of functional cementitious materials containing microencapsulated phase change materials (MEPCM). The mixture design procedure combines physics-based models with multi-objective optimization and decision-making methods to meet user’s demands on material’s mechanical and thermal properties, as well as the requirements for sustainability, functionalities, and cost. Physics-based models were utilized to draw the linkage between design variables and objective functions, including a hydration model to capture the hydration kinetics of slag-blended cement and a multiscale sub-stepping homogenization model to obtain the properties of cementitious composite. The multi-objective feasible enhanced particle swarm optimization (MOFEPSO) algorithm and the technique for preference by similarity to an ideal solution (TOPSIS) algorithm are used for mixture optimization and decision-making. The material design method is demonstrated through the design of functional cementitious composite materials containing two MEPCMs – i.e., a polymer encapsulated paraffin wax (PolyPCM) and a recently developed fly-ash cenosphere encapsulated PCM (CenoPCM). The design decision-making charts show the trade-offs among mechanical, thermal, and economic performances of cementitious composites containing MEPCMs. The mixture optimization and decision-making method can be used to assist the design of a variety types of functional cementitious composite and concrete.

Flowability and electrical properties of cement composites with mechanical dispersion of carbon nanotube

The present study aims to understand the relationship between flowability and electrical properties of cement composites with mechanical dispersion of carbon nanotube (CNT) and to establish a guideline of mix proportioning for the CNT/cement composites with suitable workability and high electrical conductivity. In this study, mixtures composed of different mix proportions and CNT types were designed, and their flow diameter, electrical resistivity, basic mechanical properties in terms of strength and elastic modulus, and microscopic morphology were measured and evaluated. Intuitive and simple modeling was performed to quantitatively assess the effect of CNT dispersibility on conductivity. The results indicated that the flowability and resistivity of cement composites were significantly affected by the dispersibility of CNTs.

Water transport and resistance improvement for the cementitious composites with eco-friendly powder from various concrete wastes

The water transport properties of cementitious composites are the key parameters to evaluate the durability performance. This work gives an investigation on the impact of RP type, substitution rate and particle size on the water transport in cementitious composites, and the feasible methods of improving the water transport resistance are further investigated. Utilizing recycled paste powder (RPP), recycled mortar powder (RMP) and recycled concrete powder (RCP) produced from various concrete waste is detrimental to the hydration reaction and pore structure of cementitious composites, and the total porosity of paste incorporating 30% various RPs is 35.4–36.0% higher than that of plain paste. Utilizing RP decreases the compressive strength of cementitious composites, and a significant reduction in compressive strength occurs when RP substitution rate is 50%. The water transport in cementitious composites is increased by incorporating RP, and the RMP-prepared and RCP-prepared mortar have lower water absorption than the RPP-prepared mortar; for example, the absorption coefficient of the mortar containing 30% RPP, RMP and RCP is 72.7%, 44.9% and 48.7% greater than that of plain mortar without RP. Besides, the water transport in the mortar incorporating fine particle RP is lower than that in the mortar containing coarse particle RP. Co-mixing RP and mineral admixtures decreases the water transport in cementitious composites, and the mortar incorporating 20% RP and 10% metakaolin (or 10% silica fume) has lower water absorption and slightly higher compressive strength than plain mortar without RP.

Effect of micro-sized silica aerogel on the properties of lightweight cement composite

Lightweight cement composite (LCC) has gained more interest and is increasingly explored by researchers due to its many advantageous properties. Silica aerogel (SA), a synthetic ultralight material, has a nano-porous structure, making it a potential option to be incorporated for LCC. Thus, this research intends to assess the influence of micro-sized SA fines on the properties of cement composite. Specifically, its effect on fresh state properties, porosity, density, compressive strength, rate of water absorption, total water absorption, wettability, and softening coefficient was investigated. The lightweight and micro-size of SA reduced the consistency and slump (up to 90%) of the fresh LCC. Besides that, its hydrophobic nature produced macropores which doubled the porosity in the cement composite. This resulted decrease in density (up to 35%), compressive strength (up to 76%), wettability (up to 21%), and softening coefficient (up to 33%). Water transport properties such as water absorption and rate of water absorption were also increased due to the formation of macropores in the SA cement composite. However, compared to some other LCCs, the cement composite produced with the SA fines in this study in overall exhibited good specific strength.

Data-driven machine learning approach for exploring and assessing mechanical properties of carbon nanotube-reinforced cement composites

Traditional experimental investigation on the mechanical properties of cement composites is deprecated due to the intensive time and labor involved. Existing predictive models can hardly map the complicated relationships among mechanical attributes and behavior. This study first adopts machine learning to predict the mechanical properties of carbon nanotube (CNT)-reinforced cement composites. For this purpose, predictive models are trained on the previously published experimental data and results demonstrate that machine learning models present better generalization ability and predictive performance than the traditional response surface methodology. A sensitivity analysis indicates that the factor having the maximum influence on compressive strength is the length of CNTs, whereas that having the maximum influence on flexural strength is the curing temperature. Thus, it can be concluded that compared with the traditional experimental investigation and regression methods, machine learning can efficiently and accurately predict the mechanical properties of CNT-reinforced cement composites.

Effect of Wood Biomass Ash Storage on the Properties of Cement Composites.

Since ash from wood biomass mostly ends up in landfills, recent research has focused on finding its economic and environmental added value as a potential new raw material in the construction industry. However, for wood ash to be used on an industrial scale in construction, a strategy for its proper storage must be defined. Proper storage of WBA is important to ensure quality control for applications in cementitious composites. This work investigated the aging of wood biomass ash (WBA) collected from five different power plants in Croatia and its influence on the performance of cementitious composites. WBA and cement pastes were investigated at different aging times (up to one year) using thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), isothermal calorimetry and initial and final setting times. The results showed that storage of WBA in closed and open containers resulted in carbonation and hydration of mainly free lime and periclase, respectively, which affected the reactivity and setting times of WBA cement pastes.

Sound-Absorbing and Thermal-Insulating Properties of Cement Composite Based on Recycled Rubber from Waste Tires

This article describes an experimental study aimed at investigating the potential use of recycled rubber granulate from waste tires of fractions 0/1 and 1/3 mm in cement composites as a 100% replacement for natural aggregates. The use of waste in the development and production of new building materials represents an important aspect for the sustainability and protection of the environment. This article is focused on the sound-absorbing and thermal-insulating properties of experimental cement composites based on recycled rubber from waste tires. The article describes the grain characteristics of recycled rubber, sound absorption capacity, thermal conductivity and strength characteristics. The results of this research show that the total replacement of natural aggregate with recycled rubber in cement composites is possible. Replacing natural aggregate with recycled rubber has significantly improved the thermal and acoustic properties of the prepared cement composites, however, at the same time; there was also the expected decrease in the strength characteristics due to the elasticity of rubber.

Physicochemical and Piezoresistive properties of smart cementitious composites with graphene nanoplates and graphite plates

Graphene nanoplate (GNP) and graphite plate (GP) are promising functional nanofillers for smart self-sensing cementitious composites. The effects of GNP and GP on physicochemical, mechanical and piezoresistive properties of cementitious composite were investigated in this paper. The results show that cement hydration was accelerated with the increased amounts of GNP and GP because of nucleation effect. The electrical resistivity of GNP-cementitious composites was always lower than the counterpart with GP with the same concentration. On the other hand, percolation occurred for the GNP/cementitious composites at the dosages from 2 to 3% (by weight), while it never happens for the GP/cementitious composites. Moreover, the GNP/cementitious composites reached the maximum mechanical strength when the GNP content was 1.0%, while for the GP/cementitious composites, only minor strength improvement was obtained with a dosage of 0.5% GP. As for the piezoresistivity, the cementitious composites with GNP exhibited higher fractional changes of resistivity. Irreversible resistivity happened for 2–3% GP/cementitious composites subjected to cyclic compression, due to the poor and loose microstructures. The outcomes are expected to provide an insight into the application of GNP/cementitious and GP/cement composites as cement-based sensors for the future structural health monitoring.

Investigation of the Effect of Seawater and Sulfate on the Properties of Cementitious Composites Containing Silica Fume

Concrete consumes over two billion tons of freshwater every year and 75 % of regions of the world will become water shortages in 2050. Because of increasing freshwater scarcity seawater may become reasonable as an alternative mixing and curing water for concrete. In this study, seawater (SW) was utilized for mixing and curing of concrete and investigated the seawater and sulfate on the properties of cementitious composites containing silica fume (SF). Hence, SF was replaced with the cement at ratios corresponding to 0 %, 2.5 %, 5 %, 7.5 %, 10 %, 12.5 %, and 15 % by weight of cement, and SW and tap water (TW) were used as mixing water in the production of cementitious composites. Thus, the effect of SW on the properties of fresh cement pastes and the flexural and compressive strengths of 7-day, 28-day, and 90-day old cementitious composites were examined. Additionally, the lengthening change values of cementitious composites containing SF that were kept in 5 % Na2SO4 solution for 7-day, 28-day, and 90-day were determined. The SF delayed the setting period while increasing the water requirement of the cement paste. It is determined that the SW accelerated the setting period of cement. In the case when 10 % SF in cementitious composites was used, the maximum compressive and flexural strengths were obtained for cementitious composites produced by mixing with SW and SF fume at an age corresponding to 28-day and 90-day. It was observed that the length change of the cementitious composites decreased due to the increase in the SF replacement ratio.

Electromagnetic shielding properties of cementitious composites containing carbon nanofibers, zinc oxide, and activated carbon powder

Exposure to electromagnetic radiation is known to cause many adverse effects such as malfunction of electronic devices and health problems in humans. Since currently used metallic shields suffer from various drawbacks, using construction materials that would provide the same amount of shielding has become a novel research area in the construction industry. Set of experiments were carried out to find the effect of carbon nanofibers, zinc oxide, and activated carbon powder on electromagnetic interference shielding in cementitious composites. Additionally, the impact of these additives on mechanical and electrical conductivity was measured. For these experiments, four different types of carbon nanofibers were used to establish the best type of carbon nanofibers. Different contents of each additive were mixed into the cementitious composite to find the optimal content of each additive. These three different types of additives were then combined with 12 mm unsized carbon fibre within the cementitious matrix. Effects of the hybrid composites were measured similar to previous tests to find out the best combination of additives that would provide the optimum amount of electromagnetic shielding. Electromagnetic shielding tests were carried out within the frequency range of 30 MHz to 1.5 GHz according to ASTM D4935 – 18 standard method. Results showed that the inclusion of individual additives did not have a significant impact on the electromagnetic shielding properties. The best shielding properties were obtained when 0.5% of activated carbon powder was combined with the carbon fibre, which was 42.5–60.0 dB.

Radiative cooling potential of cementitious composites: Physical and chemical origins

Passive radiative cooling includes spontaneously cooling a structure by reflecting and emitting light through atmospheric window (8 μm–13 μm) into the cold universe. This paper involves a systematical study on maximizing the radiative properties of cementitious composites by optimizing constituents and microstructures. Relatively high hemispherical solar reflectance (82 ± 2) % and middle infrared (MIR) emissivity (87 ± 2) % were achieved simultaneously, allowing for an inner temperature drop of 12 °C in field test. Whiter surface, micro-magnitude pore size and TiO2 particle diameter all lead to higher reflectance in visible and near-infrared (VIS- NIR, 0.4 μm–2.5 μm) region. From the hydration products, complex infrared absorbance of O–H bonds yields low reflectance, while O–H, Si–O, Si–O–Si bonds stretching vibrations guarantee high emissivity. CaCO3, whether added as admixture or formed by carbonation, significantly increases the VIS reflectance. Both numerical simulation and field test demonstrate great potential of utilizing radiative cooling cementitious composites for building energy saving.

Nanomaterials in Cementitious Composites: An Update.

This review is an update about the addition of nanomaterials in cementitious composites in order to improve their performance. The most common used nanomaterials for cementitious materials are carbon nanotubes, nanocellulose, nanographene, graphene oxide, nanosilica and nanoTiO2. All these nanomaterials can improve the physical, mechanical, thermal and electrical properties of cementitious composites, for example increase their compressive and tensile strength, accelerate hydration, decrease porosity and enhance fire resistance. Cement based materials have a very complex nanostructure consisting of hydration products, crystals, unhydrated cement particles and nanoporosity where traditional reinforcement, which is at the macro and micro scale, is not effective. Nanomaterials can reinforce the nanoscale, which wasn’t possible heretofore, enhancing the performance of the cementitious matrix.

Enhanced workability, durability, and thermal properties of cement-based composites with aerogel and paraffin coated recycled aggregates

The use of construction and demolition (C&D) wastes in building materials is a key step toward a sustainable construction industry. In this context, the application of recycled concrete aggregates (RCAs) in cement composite mixtures has been investigated by various researchers. The results available in the literature indicate that cement mortar adhered to the surface of RCAs leads to high water absorption and large porosity in cementitious mixtures. As a result, lower workability, durability, and mechanical properties in comparison to conventional aggregates are often known as the main attributes of mixtures containing RCAs. Additionally, improving the thermal energy storage capability of RCAs by using high-performance thermal insulation materials, such as phase change materials (PCMs) and aerogel can assist in minimizing the energy consumption in buildings. Accordingly, this paper aims at characterizing RCA mixtures with enhanced workability, durability, and thermal properties. The effect of using paraffin coated recycled concrete aggregates (PCRAs) and aerogel aggregates on the mechanical, thermal, and durability properties of cement composites are investigated in this paper. Results of dry density, compressive strength, water absorption content, permeable voids, thermal conductivity, rapid chloride migration test (RCMT), capillary water absorption, and scanning electron microscopy (SEM) tests along with energy-dispersive X-ray spectroscopy (EDX) are reported to evaluate the effect of several variables on the investigated concrete mixtures. Results of the conducted tests indicate that using PCRA significantly improves the durability characteristics of mixtures such as water absorption content, permeable voids, and RCMT, while it slightly decreases the compressive strength of mixtures with respect to the control mixture. In addition, aerogel aggregates significantly improve the thermal conductivity of mixtures while reduced the mechanical and durability characteristics.

Review of recent developments in cement composites reinforced with fibers and nanomaterials

The quest for high-performance construction materials is led by the development and application of new reinforcement materials for cement composites. Concrete reinforcement with fibers has a long history. Nowadays, many new fibers associated with high performance and possessing eco-environmental characteristics, such as basalt fibers and plant fibers, have received much attention from researchers. In addition, nanomaterials are considered as a core material in the modification of cement composites, specifically in the enhancement of the strength and durability of composites. This paper provides an overview of the recent research progress on cement composites reinforced with fibers and nanomaterials. The influences of fibers and nanomaterials on the fresh and hardened properties of cement composites are summarized. Moreover, future trends in the application of these fibers or of nanomaterial-reinforced cement composites are proposed.