Shrinkage Of Composites Research Articles

Polymerization shrinkage of composites with different viscosities

Polymerization shrinkage of composites with different viscosities

Restraint effect of steel bar on early-age shrinkage of steel bar-mortar composites

Time-space-dependent stress and strain distribution within steel bar-mortar composites is key for shrinkage and cracking prediction of Reinforced-Concrete (RC) members. A novel system was designed to investigate the restraint of steel bars on the early-age shrinkage while digital image correlation was also employed to analyze spatial strain distribution. The measured restraint degree increases with the reinforcement ratio and maintains stable after about 36 h. Restraint effects is interfered by micro-cracks, because of which the calculated restraint degree matched the measured one better after being modified by a coefficient concerning reinforcement ratio. The overall restrained stress shows a three-stage process affected by the bonding evolution. The strain spatially undergoes a three-region distribution along the steel bar induced by the shear transfer and a two-region distribution on the cross-section aligning with the interface gradient. This study demonstrates a quantitative analysis on the steel bars restraint parameters and its evolution.

Impact of chitosan extracted from shrimp shells on the shrinkage and mechanical properties of cement-based composites using dendritic fibrous nanosilica

Dendritic fibrous nanosilica (DFNS) was functionalized using microcrystalline chitosan, derived from shrimp exoskeletons, to act as a robust anchor, resulting in DFNS@Chitosan. In order to prevent the restacking of chitosan sheets, the supramolecular polymerized chitosan not only served as a spacer but was also incorporated into cement-based composites. The physical-chemical characteristics of DFNS@Chitosan were assessed through various analytical techniques such as TEM, SEM, TGA, FTIR, AFM, XPS, and EDX. The potency and auto-induced contraction of Cement-based composite materials fortified with DFNS@Chitosan were probed. The incorporation of DFNS@Chitosan resulted in an increase in both compressive and interfacial stretching potency of the cement-based composites. Furthermore, the presence of DFNS@Chitosan effectively inhibited the occurrence of auto-induced contraction in the cement-based paste. This research endeavor is anticipated to promote an alternative utilization of DFNS and shrimp waste shells in the development of sustainable building materials.

Effect of crystalline admixtures on shrinkage and alkali-silica reaction of biochar-cementitious composites

This study investigated effects of crystalline admixture (CA) on shrinkage and alkali-silica reaction behaviours of biochar-cementitious composites. Addition of 1–1.5 wt% superabsorbent polymer (SAP) completely mitigated autogenous shrinkage while slightly increasing the 120-day total shrinkage of the SP-cement composite by 5.7%, resulting in the highest apparent porosity. 1–1.5 wt% CA addition did not affect autogenous shrinkage while slightly reducing the 120-day total shrinkage by 10.1%. The combination of CA and waste wood biochar (WWB) reduced autogenous shrinkage by 24.23% and 120-day total shrinkage by 23.6%, resulting in the lowest apparent porosity. The formation of hydration products in the WWB pores and on WWB surface densified the cementitious matrix, leading to a reduction in water evaporation. Furthermore, for specimens exposed to 1 M NaOH solution at 80 °C, CA addition significantly reduced the 120-day expansion by 50.6%, while the combination of CA and WWB addition reduced the 120-day expansion by 42.9%.

Drying Shrinkage and Mechanical Strength of Cementitious Composites with Alkali-Treated Makino Bamboo Fibers

ABSTRACT Alkali-treated bamboo fibers (AFs) treated with different NaOH concentrations (5 and 10%) and treatment times (1, 12, and 24 h) were used as fillers to fabricate cementitious composites with AFs (CAFs) in the present study. The results demonstrated that alkali treatment caused the partial decomposition of hemicellulose and lignin and an increase in the surface roughness of bamboo fibers. Additionally, the amounts of calcium hydroxide in alkali-treated CAFs were higher than in untreated CAFs, and they increased with increasing NaOH concentration and treatment time. For drying shrinkage (DS) under 75% relative humidity (RH), the DS values of the CAFs significantly decreased after adding AFs compared to the DS values of untreated CAFs. Compared to untreated CAFs, the density of the 5% and 10% NaOH-treated CAFs with longer treatment times decreased by 2.9% and 5.1%, respectively. Furthermore, the tensile strength of all alkali-treated CAFs exhibited no significant differences when compared with that of untreated CAFs, while the modulus of rupture and compressive strength were significantly decreased by NaOH treatment. These results indicated that the AFs significantly improved the drying shrinkage of the CAFs and hydration retardation effect of cement pastes, while the density and mechanical strength of the CAFs decreased.

A Review on Chemical and Autogenous Shrinkage of Cementitious Systems.

Chemical shrinkage (CS) is an intrinsic parameter that may affect the early age cracking of paste, mortar and concrete. It is well known as the driving force of self-desiccation, autogenous shrinkage (AGS) and drying shrinkage. During the first stage of cement hydration (at the initial setting time), the CS and AGS are equal. In the hardened stages, there is a difference in values between the two shrinkage parameters. This paper is a comprehensive review on CS and AGS, measurement techniques, modeling and prediction of different cementitious systems. Based on the various experimental studies, chemical shrinkage depends on the water to binder ratio (w/b) and is proportional to the degree of hydration. A low w/b ratio leads to high CS and AGS. The composition of cement has an effect on both CS and AGS. Also, incorporating supplementary cementitious materials (SCMs) affects both shrinkage parameters. It is concluded that adding fly ash (FA) to concrete contributes to CS and AGS reductions. However, this is not the case when concrete contains slag. More than 170 references were consulted including 35 which were published after 2020. According to the authors knowledge, there is no published work on the effect of fibers, especially bio-fibers, on the chemical shrinkage of cement-based composites. Therefore, in addition to traditional chemical shrinkage of cementitious systems, this review includes a section on recent papers conducted by the authors on the effect of bio-fibers on the chemical shrinkage of cement composites.

Dynamic and Relaxation of PEG polymer Chain Segment for Phase Change Materials (PCMs)

This work’s most notable memory concept for next-generation novels was a reversible phase shift in a substance called phase change materials (PCMs). Here, a polyethylene glycol (PEG) polymer relaxation study employing DMA will be conducted to investigate the qualities of PCMs as superior materials. Through the method of wet mixing, PEG polymer with reinforcement made of silica was synthesized. The variation of silica xerogel was a composition of up to 20% silica xerogel. Adding silica is quite good in reducing the loss factor up to 50 MPa at the addition of 20% silica xerogel. This condition was due to the bonds formed in the polymer chain causing shrinkage and flexibility of composites. Due to the addition of silica xerogel as filler, we can study the relaxation behavior and loss factor of a material using DMA and learn more about its viscoelastic characteristics, including its capacity to absorb vibrations, resistance to impacts, and overall mechanical performance at various temperatures. Relaxation was frequently used to describe phase change materials (PCMs), especially when discussing their capacity to store thermal energy. The release or absorption of thermal energy by a PCM during its phase transition was referred to as the relaxation process.

Role of fiber dosages and lengths on the mechanical strength, shrinkage, and pore structure of CO2-cured amorphous metallic-fiber-reinforced belite-rich cement composites

The impact of varying dosages and lengths of amorphous metallic fiber (AMF) on the mechanical strength, shrinkage, and pore structure of fiber-reinforced cementitious composites cured in water and in a carbonation chamber were assessed. This study evaluated fourteen mortar mixes, i.e., seven mixes for traditional water curing and seven for CO2-curing (60% relative humidity, 20 °C, and 10% CO2 concentration). The outcomes reveal that the compressive and flexural strength are significantly augmented for the mixes reinforced with AMFs as compared to the control mix (fiber-free mix), and this behavior is more pronounced with increased dosages and lengths of the AMF. Furthermore, compared to the control mix, significant mitigation in the development and magnitude of shrinkage was recorded with increased dosages and lengths of the AMF. The porosity and voids were all increased in the samples with AMF as compared to the control mix. The carbonation-cured specimens exhibited significantly higher mechanical strength, fewer voids, and higher shrinkage than those cured in water. Based on the experimental findings, it is recommended to use 0.50% volume of AMF and a length of 20 mm to produce fiber-reinforced cement composites, as this combination provides outstanding performance among all mixes tested here.

Measuring polymerization shrinkage of dental composite by using PhS-OCT

A method based on phase-sensitive optical coherence tomography (PhS-OCT) was developed to investigate the depth-resolved polymerization shrinkage of dental composites. The method uses optical coherence tomography (OCT) system to acquire the interference spectra during dental composite polymerization and then estimate the refractive index variation and shrinkage strain from the phase variations of the acquired spectrum. Since OCT is a tomographic imaging technique, PhS-OCT is also available for imaging full-field polymerization behavior inside dental composites. For validation, the polymerization processes of three dental composites, FiltekTM Z350, FiltekTM Z250 and FiltekTM P60, were monitored with PhS-OCT. The strain results agree with the reference values and the relative errors are less than 10%. In addition, the vitrification-point delayed curves were measured, revealing the vitrification-point retardation phenomenon. Finally, the flowable dental composite that polymerized inside the human artificial tooth was also measured, successfully demonstrating the depth-resolved full-field polymerization behavior inside the dental composite.

Effect of calcined zeolite on the shrinkage and mechanical properties of lightweight engineering cementitious composites

Lightweight engineering cementitious composites (LECCs) show great promise for weight-sensitive structures such as bridges, high-rise buildings, and floating platforms. However, the large quantities of cement used in LECCs cause significant shrinkage, which leads to debonding of LECCs from the original structural interface during structural strengthening and repair, severely compromising its strengthening efficiency. To address this issue, we investigated the use of zeolite as an internal storage source to compensate for water loss during the hydration of LECCs, focusing on the relationship between the mechanical and dry-shrinkage properties of LECCs after the introduction of zeolite. XRD and SEM were used to reveal the microscopic mechanisms of zeolite action in the LECC matrix. The results showed that the compressive and tensile strengths of LECCs were improved by the internal care of the zeolite, and the optimum strength was achieved with 5% zeolite addition. In addition, zeolite doping significantly improved the drying shrinkage of LECCs, which was reduced by 31.2% at a 2.5% replacement compared with that of the control group. Microscopic analysis showed that the reduction in shrinkage and increase in strength of the LECC matrix were mainly attributed to the role of the volcanically active zeolite in the later stages of cement hydration, which provided sufficient water to promote further hydration of the hydration products, resulting in a slightly swollen dense microstructure such as that of hydrated calcium silicate aluminate.

Hardened properties and microstructure change of sulphoaluminate cement modified with different doses of styrene-butadiene rubber latex

The composite of sulphoaluminate cement (SAC) and styrene-butadiene rubber (SBR) latex is expected to possess rapid strength development and adjustable elastic modulus, mainly used in rush repair engineering. This paper investigates the mechanical strength and drying shrinkage of SBR-SAC composites with different proportions. The change of pore structure, phase composition, and microtopography behind the composites was further revealed. Results indicate that, when the SBR/SAC ratio increases from 0/10 to 3/10, the flexural strength of the composite is increased by 343% and its compressive strength is increased by 14.7%, the drying shrinkage is almost not considered, below 0.1%. Besides, at the SBR/SAC ratio of 5/10, the composite loses brittleness, with no obvious peak value of load–displacement curves, and the drying shrinkage of composite at 23 d is 1.496%. This is because dehydrated polymer occupies the location of SAC hydrates, and the polymer film gradually and continuously covers the surface of the cement and becomes thickened. With the increasing SBR/SAC ratio, the continuous phase of composite probably transforms from inorganic cement phase to organic polymer phase.

Assessment of shrinkage and bond behaviour of high performance cement-based composites as a repair mortar

There is a need to develop innovative repair materials which can overcome the challenges of cement-based repair mortars being relatively prone to shrinkage effects. In practice, free shrinkage of repair mortar is often considered as an indicator for potential cracking and delamination of applied repair mortars due to restrained shrinkage effects. As it is hard to measure restrained shrinkage directly, a restraint factor (R) can be used to correlate both. This study investigates the shrinkage characteristics of strain-hardening cementitious composites (SHCC), making use of polyvinyl-alcohol (PVA), high-density poly-ethylene (HDPE), or short glass fibres, for the repair and strengthening of existing concrete structures. Along with drying shrinkage and autogenous shrinkage, restrained shrinkage has been characterized with respect to the concrete substrate. Furthermore, pull-off tests were performed to assess the bond properties of these repair mortars. The results show around 65% higher autogenous shrinkage in high strength SHCC mixes while there was a decrease in drying shrinkage compared to the reference mix. In contradiction to what was initially expected, an increase in fibre content from 1.5 to 2.0 vol% resulted in a significant increase in autogenous shrinkage, especially in the high strength SHCC mixes. The restraint factor for all repair mortars was determined and was found to be in the range of 0.82–0.94. The pull-off tests showed an overall excellent bond behaviour of all studied mortars.

Polymerization shrinkage of light-cured conventional and bulk-fill composites -The effect of cavity depth and post-curing.

Volumetric shrinkage (VS) of conventional, bulk-fill, and core build-up resin-based composites (RBCs) of various thickness (1-5 mm) was measured using the modified bonded-disk method with confocal laser scanning microscopy. Additionally, the bottom-to-top ratio of Vickers hardness (%VH) was measured. Conventional RBCs exhibited significantly higher VS than bulk-fill and core build-up RBCs (p<0.05). As specimen thickness increased, VS relative to volume (%VS) and difference in VS at each depth (VSdepth) decreased. For conventional RBCs, there was a significant drop in VSdepth between 1 mm and 2 mm (p<0.05), and another drop was observed between 3 mm and 4 mm (p<0.05) where %VH decreased below 90%. For bulk-fill and core build-up RBCs, VSdepth decreased significantly between 2 mm and 3 mm (p<0.05), but %VH exceeded 90% even in 5 mm deep cavities. These results indicated that post-curing contributed to lower shrinkage in deeper layers, and that conventional RBCs were not adequately polymerized at the depth of over 3 mm.

The effect of high-irradiance rapid polymerization on degree of conversion, monomer elution, polymerization shrinkage and porosity of bulk-fill resin composites.

The purpose was to compare the degree of conversion (DC), monomer elution (ME), polymerization shrinkage (PS) and porosity of two addition-fragmentation chain transfer (AFCT) modified resin-based composites (RBC) light-cured with rapid- (RP), turbo- (TP) or conventional polymerization (CP) settings. Cylindrical samples (6-mm wide, 4-mm thick) were prepared from Tetric PowerFill (TPF) and Filtek One Bulk (FOB). Four groups were established according to the polymerization settings: 3s-RP, 5s-TP, 10s-CP and 20s-CP. Samples in 1mm thickness with 20s-CP settings served as controls. The DC at the top and bottom surfaces was measured with micro-Raman spectroscopy. ME was detected with high-performance liquid chromatography. PS and porosity were analyzed by micro-computed tomography. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p<0.05). FOB showed higher DC values (61.5-77.5 %) at the top compared to TPF (43.5-67.8 %). At the bottom TPF samples achieved higher DCs (39.9-58.5 %) than FOB (18.21-66.18 %). Extending the curing time increased DC (except the top of FOB) and decreased ME. BisGMA release was the highest among the detected monomers from both RBCs. The amount was three-fold more from TPF. The factor Material and Exposure significantly influenced DC and ME. PS (1.8-2.5 %) did not differ among the groups and RBCs except for the lowest value of TPF cured with the 3s_RP setting (p=0.03). FOB showed 4.5-fold lower porosity (p<0.001). Significantly higher pore volume was detected after polymerization in 3s_RP (p<0.001). High-irradiance rapid 3-s curing of AFCT modified RBCs resulted in inferior results for some important material properties. A longer exposure time is recommended in a clinical situation.

Asses the Use of Calcium Carbide for Increasing Mechanical and Thermal Properties of Alkali Activated GGBFS-MK Precursor

The purpose of this paper is to investigate whether calcium carbide can effectively develop the strength of a slag-metakaolin geopolymer matrix. For all mixes, a solution of sodium hydroxide and sodium silicate was used as a liquid alkali activator. CaC2 was added in ratios of 0, 0.5, 1.0, 1.5, 2.0 and 2.5% by weight. Compressive strength shrinkage and thermal resistance of alkali-activated composites were examined. The GGBFS-MK geopolymer pastes with/without calcium carbide were subjected to FTIR, XRD, and SEM investigations for inspecting the effect of the CaC2 addition. The findings demonstrated that calcium carbide enhances compressive strength compared to the control mix, by producing more reaction products and providing a greater level of geopolymerization.

Influence of industrial by-product sulfur powder on properties of cement-based composites for sustainable infrastructures

The use of industrial by-products has attracted much attention globally in recent years because of the improved durability and sustainability of cement-based composites. To promote the application of sulfur powder (SP) in cement-based composites, a new hydrophilic modified sulfur powder (MSP) was prepared in this paper. The effects of unmodified sulfur powder (NSP) and MSP on workability, strength, permeability, dry shrinkage, and frost resistance of cement-based composites were thoroughly studied. Based on microstructural evolution, hydration heat, hydration product composition, and pore structure, the modification mechanism of NSP and MSP on cement-based composites were investigated. The results show that adding NSP improves the fluidity of cement-based composites while adding MSP has the opposite effect. An appropriate amount of MSP and NSP improves the durability of cement-based composites. However, both NSP and MSP reduce the 28d strength of cement-based composites. Compared with NSP, the incorporation of MSP reduces the hydration release rate, refines the pore structure, and improves the interface bond with the cement matrix. This study deepens our understanding of the influence of SP on the fundamental properties of cement-based composites, which also provides new perspectives on creating a sustainable built environment.

Analysis of variance of injection moulding process parameters and clay particles size effects on impact strength, shrinkage and warpage of polyethylene/kaolin clay composites

A correlation effect between particle size of kaolin clay and injection moulding process parameters on impact strength, shrinkage and warpage of high-density polyethylene/kaolin clay (HDPE/KC) composites was carried out using analysis of variance (ANOVA). Kaolin clay with particle sizes of < 75, 75–106 and 106–150 μm was used. The process parameters that were taken into consideration were injection temperature, packing pressure and packing time. In general, experimental results showed that the impact strength and shrinkage of the HDPE/KC composites clearly depended on the injection temperature. However, no clear dependency of the warpage on the injection temperature was observed. Furthermore, clay particle size showed to have an influence only on the shrinkage of the composites, where smaller clay particle size led to injected composite parts with relatively less shrinkage. ANOVA showed that the effect of injection temperature on shrinkage of composites containing clay particle sizes of < 75 and 106–150 μm was statistically significant (p = 0.01 and 0.04, respectively). However, the effect of injection temperature on shrinkage of the composite made with clay having particle sizes of 75–106 μm was not significant (p = 0.07). ANOVA also indicated that the injection temperature effect on the impact strength of composites that contain clays with particle sizes of < 75 μm and 75–106 μm was significant (p = 0.03 and p = 0.01, respectively), whereas the injection temperature effect on the impact strength of the composite containing clay with a particle size of 106–150 μm was not significant (p = 0.17). Contrary to shrinkage and impact strength, the effect of the studied parameters on the warpage was not statistically significant, which was in good agreement with the experimental observations.

The impact of natural fibers’ characteristics on mechanical properties of the cement composites

The paper reviews the properties of cement composites reinforced with short fibres. The effect of natural fibres was investigated: cotton, sisal, jute, ramie, bamboo, and synthetic fibres: polymer and polypropylene. It was noticed that the fibres change the consistency of the mixture up to 15%. In the composite flexural strength tests, a change in strength by +/− 8% was observed, depending on the type of fibres used. The research shows that the use of natural fibres had a positive effect on the compressive strength by 27%, while the use of synthetic fibres caused its decrease by 4%. Additionally, it was noticed that the chemical composition, the diameter and the total length of the fibres in the element have an impact on the composite shrinkage. The fibre-containing composites showed an 8% higher water absorption compared to the non-fibre samples. The exception is the ramie fibres, which reduce water absorption. In general, a positive effect of natural fibers on the properties of cement composites has been noticed, however, in case of natural fibres application, a thorough further properties investigation is recommended.

Impact of polyvinyl alcohol fiber on the full life-cycle shrinkage of cementitious composite

Engineered cementitious composite (ECC) enjoys huge potential in building structures thanks to its excellent tensile performance and energy absorption ability. However, free deformation of ECC deserves better understanding since large shrinkage strain usually induces internal tensile stress which would lead to cracking under constraint. Present study focuses on the full life-cycle shrinkage of polyvinyl alcohol (PVA) fiber reinforced ECC. Shrinkage and relative humidity (RH) at three water to cement (w/c) ratios were experimentally tested through novel integrated deformation measurement device. In contrast, plain mortars with the same w/c ratios were compared to evaluate the impact of PVA fiber on the over-time deformation and RH characteristics. Thereafter, shrinkage model considering fiber influence coefficient is established to simulate autogenous and drying shrinkage of PVA-ECC. Results show that full life-cycle shrinkage can be divided into two stages according to the internal RH measured. Distinct restraint effect of PVA fiber on both stages are observed. By comparing experimental and simulation results of PVA-ECC, the proposed fiber influence coefficient-based shrinkage model well illustrates the effect of PVA fiber, especially for high strength cementitious composites with relatively low w/c.

Relationship between the fineness and specific surface area of iron tailing powder and its effect on compressive strength and drying shrinkage of cement composites

The management and reuse of iron tailings (ITs)not only help protect the environment but also are linked to the reduction of cement consumption. The preparation of supplementary cementitious material (SCM) through iron tailings powder (ITP) has shown promising prospects. In this paper, the relationship between fineness levels and the specific surface area of ITP and its effect on the drying shrinkage behavior and compressive strength of cement composites were studied. The results show that with increasing grinding time, the relationship between particle fineness levels and the specific surface area of ITP is not linear, and the pozzolanic activity of ITP is related to its surface area. Due to the pozzolanic activity and filler effect of ITP, the addition of ITP with a large specific surface area increases the formation of hydration products in the later stage of blended cement paste and refines the pore structure. The pozzolanic activity of ITP increases with increasing ITP specific surface area, and obtain stronger compressive strength growth at later ages. Moreover, there is a linear relationship between the activity index of ITP and the specific surface area of ITP. ITP in blended mortar plays a key role in limiting drying shrinkage, which is positively related to its specific surface area, and it had a long-term volume stability trend than cement-based mortar.