Polycarboxylate Ether-based Superplasticizer Research Articles

A potential active rheology control approach for 3D printable cement-based materials: Coupling of temperature and viscosity modifiers

Recently, the active rheology control for 3D printable cement-based materials (3DPCM) has gained increasing attention due to the challenging rheological requirements during printing. Inspired by the influences of polymers on the temperature sensitivity of rheological properties, here we propose a concept of active rheology control for 3DPCM coupling temperature control with the utilization of viscosity modifiers. Firstly, the rheological properties associated with 3D printing in response to a temperature range from 5 °C to 45 °C were investigated through flow curve, stress growth and small-amplitude oscillatory shear tests. Subsequently, total organic carbon and isothermal calorimetry tests were performed to further analyze the mechanism. Finally, validation 3D printing tests were conducted. Results indicate that increasing temperature improves the efficacy of hydroxypropyl methylcellulose and polycarboxylate ether-based superplasticizer through accelerated dissolution and adsorption, and enhanced chain stretching, thus allowing for an intensified or a suppressed response to temperature in the apparent viscosity, thixotropic area, static yield stress and storage modulus of 3DPCM. Increasing temperature also compensates for the delay in cement hydration due to the addition of polymers. Printing experiments provide preliminary evidence of the feasibility of active rheology control for 3DPCM through coupling between temperature and viscosity modifiers to improve the printability. The thickness ratio and width ratio of top layers to bottom layers of 3DPCM with HPMC were 1.46 and 0.84 when printed at 25 °C, which are 14.1% lower and 58.3% higher compared to that printed at 15 °C.

Effect of silica fume and PCE-HPMC on LC3 mortar: Microstructure, statistical optimization and life cycle Assessment

With immense carbon emissions, the cement and concrete industries account for nearly eight percent of the world’s total. As the demand for urbanisation increases, the carbon footprint of the industry will also increase rapidly. A sustainable and greener low carbon cement called limestone calcined clay cement (LC3) is being developed as a promising alternative to ordinary Portland cement (OPC). The present study investigates the effects of silica fume (SF) on LC3 with variable dosages of polycarboxylate ether-based superplasticizer (SP) and hydroxypropyl methylcellulose (HPMC) admixtures. Using three level-three factorial (33) Box Behnken Design and response surface methodology (RSM), SF content, SP content, HPMC content, and flow value were set as input parameters to optimise and evaluate the eight output response parameters, namely, water binder (w/b) ratio, compressive strength (7 and 28 days), modulus of rupture, porosity, water absorption, ultrasonic pulse velocity, and water sorptivity. With a combined desirability of 90.8% for an optimised mix, the model showed that with 0% SF, 0.811% SP, 0.923% HPMC, and 124.12 mm of FV, a LC3-50-based cement system with higher physico-mechanical properties can be developed. The microstructural analysis was also conducted through a scanning electron microscope (SEM), Thermogravimetric Analyzer (TGA), and X-ray diffraction (XRD). The results showed Calcium silicate hydrate (C-S-H) development along with consumption of portlandite (CH) for LC3-50-based cement systems. Sustainability analysis of LC3-based mortar in terms of carbon emissions showed a 33.82% reduction in CO2 emissions as compared to OPC.

Dispersion of hydrophobic waste amorphous carbon powder in cementitious environment and its effect on the permeability of cement paste

A Proper dispersion of powder-based hydrophobic admixtures in cementitious composites is challenging due to the presence of water. Studies have shown that amorphous carbon powder (ACP), a hydrophobic by-product of refining waste materials of paraffin production can be used as a hydrophobic agent. However, mixing methods and dispersing agents for modifying cementitious materials with ACP can significantly impact their mechanical properties, workability, water-repellency (hence the durability), and dispersion quality of ACP. Lack of information about the extent of their impact on different aspects mentioned above can hinder the practical use of ACP as a hydrophobic agent. To fill this gap, the objective of this study is to comprehensively investigate factors in the dispersion of ACP in cementitious materials and the tradeoff between mechanical properties and water permeability of ACP-modified cementitious materials when more than one mixing method is adopted. The impacts of different dispersing agents and mixing methods, including ultrasonication, dry mixing, and after mixing, on dispersion quality of ACP in cementitious environment analogous with aqueous solutions and hardened cement paste were assessed. Polycarboxylate ether-based superplasticizer (PCE) proved to be the most effective dispersing agent. Compressive strength of ACP modified cement paste can be increased or decreased with or without the workability reduction effect of ACP along with PCE respectively. Based on volume fraction of ACP clusters in X-ray micro-CT 3D reconstruction of hardened cement paste, ultrasonication was identified as the most effective mixing method and dry mixing was the worst in terms of achieving a uniform distribution of ACP in cement paste. However, all mixing methods presented more than 85% volume fraction of uniformly dispersed ACP areas with no major difference in terms of hydrophobic modification capability. Modifying cement paste with a higher amounts of ACP (5 to 15% by weight of cement) substantially increased water contact angle (up to 171% for w/c ratio of 0.35) and decreased water absorption. The hydrophobic modification capability of ACP increases with a decrease in the quality of cement paste and is diminished by the presence of PCE. Consequently, without PCE, water absorption rate was reduced by up to 92% in similar ACP modified cement paste samples, which also led to a major reduction in compressive strength.

Mixture Design of High-Strength Geopolymer Concrete

In the present day, the primary issue associated with the use of Ordinary Portland Cement-based concrete is the emission of CO2. This type of concrete has a significant adverse environmental effect due to the substantial release of carbon dioxide during the calcination of limestone and the combustion of associated fuels. These processes are responsible for approximately 6–9% of the global anthropogenic greenhouse gas emissions.Geopolymer concrete serves as a viable substitute for traditional Portland cement-based concrete, as it is created through the interaction of aluminosilicate-rich source materials with highly alkaline solutions. By utilizing geopolymer concrete made from pulverized fuel-ash and ground granulated blast furnace slag (GGBFS), it becomes possible to decrease the carbon footprint and, consequently, mitigate the greenhouse effect.The main objective of this study is to develop high-strength geopolymer concrete suitable for road pavements. The materials used for this purpose includes fly ash, Ground Granulated Blast Furnace Slag, coarse and fine aggregates and alkaline solutions. Specifically, sodium hydroxide (NaOH) with a molarity of 12 and sodium silicate (Na2SiO3) in a 1:2 ratio are the chosen alkaline liquids for the geopolymerization process. Water is also incorporated, and a poly-carboxylate ether-based superplasticizer is employed to enhance the workability of fresh fly-ash-based geopolymer concrete. The compressive strength targeted in this research is M60 for the high-strength geopolymer concrete.

Compatibility of Ether-Based Poly-Carboxylate Superplasticizer with Mineral Admixtures Blended with OPC

The marsh cone test is a defined procedure to determine the quantitative fluidity of cement with mineral admixtures along with the saturation dosage and the efficiency of the superplasticizer (SP). In the present study, three mineral admixtures, micro-silica (MS), fly ash (FA), and ground granulated blast furnace slag (GGBFS) were used as cement replacement. Poly-carboxylate ether-based superplasticizer was used as a chemical admixture. Blends of cement and mineral admixtures with water/binder (w/b) ratios ranging from 0.40 to 0.60 at every interval of 0.05 were examined against the different dosages for SP. All the binder mixes reached a saturation dosage for SP, after which there is no change in the fluidity of the mix. The obtained dosage is considered the maximum amount of SP added to the concrete with the respective binder type. The replacement percentage of cement with mineral admixture also affected the fluidity of the binder mix. A decrease in the fluidity of binder mix was observed on increasing the amount of mineral admixture in it. At a higher w/b ratio, a significantly less SP dosage is required to attain saturation point and vice-versa. Based on the experimental investigation, it is concluded that the efficiency of SP depends on its dosage, the w/b ratio, the type and amount of mineral admixture.

Influence of superplasticizer on workability and strength of ambient cured alkali activated mortar

Alkali activated materials contain aluminosilicates, which can be used for building with a low environmental impact by repurposing waste resulting in cost-effective construction. The impact of nature and superplasticizer dosage on fly ash slag-based ambient cured mortar activated with sodium silicate and sodium hydroxide is not yet definitive. This paper studies the influence of various superplasticizers on fly ash-based ambient cured mortar activated with sodium silicate and sodium hydroxide. The effect of superplasticizers was evaluated by adding various superplasticizers including melamine, polycarboxylate ether and naphthalene-based superplasticizers in different dosages from 0 to 3% at 0.5% intervals. Fresh properties of alkali-activated mortar with various percentages of superplasticizer were tested using flow table apparatus and compared with mortar without superplasticizer. The hardened property of the alkali-activated mortar was tested by checking the compressive strength of the mortar cube. From the test results, naphthalene and polycarboxylate ether-based superplasticizers are compliant with alkali-activated mortar. Melamine-based superplasticizer shows a slight reduction on strength of alkali-activated mortar. In the ambient cured mortar, the optimum concentration for naphthalene and polycarboxylate ether-based superplasticizers is 2.0 percent, whereas melamine-based superplasticizer exhibits maximum strength for 2.5 percent. Even though naphthalene and polycarboxylate-based superplasticizers are effective for alkali-activated mortar, the most efficient type is the polycarboxylate ether-based superplasticizer.

Adsorption properties of polycarboxylate ether-based superplasticizer on cement particles and their resultant dispersion

Adsorption properties of polycarboxylate ether-based superplasticizer on cement particles and their resultant dispersion

Investigating the effect of polycarboxylate-ether based superplasticizer on the microstructure of cement paste during the setting process

There is limited measure available to quantify the effect of polycarboxylate-ether based superplasticizer (PCE) on the microstructure of cement-based systems during the first 24 h. To fill this gap, the backscattered electron image analysis (BSE-IA) alongside the ternary technique is used in this study to separate composed phases quantitively and then calculate the average spacing between cement particles. Besides, together with an examination of hydration heat, the skeleton development of reaction products is investigated. The results show that cement hydration is not a constant process, and the developing mode for hydration products region varies with the particle size of cement. In this regard, numerous hydration products may gather around small cement particles and then adsorb other unhydrated particles, forming the continuous region. By contrast, the particles possessing relatively large size are surrounded by noticeable pores, which interrupt the continuity of the hydration products region. When introducing PCE, the agglomeration of cement particles and the average spacing between cement particles reduced, manifesting as an enlarged hydration products region alongside a decreased porosity at the area surrounding large particles. However, this leads to a decreased hydration degree for cement and extends the setting time of cement paste.

Insight into Saturated Hydraulic Conductivity of Cemented Paste Backfill Containing Polycarboxylate Ether-Based Superplasticizer

Recycling of tailings in the form of cemented paste backfill (CPB) is a widely adopted practice in the mining industry. Environmental performance is an important design criterion of CPB structures. This environmental performance of CPB is strongly influenced by its saturated hydraulic conductivity (permeability). Superplasticizers are usually added to improve flowability, but there is a limited understanding of their influence on the hydraulic properties of the CPB. This paper presents new experimental results on the variations of the hydraulic conductivity of CPB containing polycarboxylate-based superplasticizer with different compositions and curing conditions. It is found that the hydraulic conductivity of the CPB decreases with the addition of superplasticizer, which is beneficial to its environmental performance. The reduction is largely attributable to the influence of the ether-based superplasticizer on particles mobility and cement hydration. Moreover, both curing temperature and time have correlations with the hydraulic conductivity of CPB containing superplasticizer. In addition, the presence of sulfate and partial replacement of PCI with blast furnace slag reduces the hydraulic conductivity. The variations are mainly due to the changes in the pore structure of the CPB. The new results discussed in this manuscript will contribute to the design of more environmental-friendly CPBs, which is essential for sustainable mining.

Workability adjustment and sensitivity of different fine cement mixtures to polycarboxylate ether-based superplasticizer

From previous studies, the most effective superplasticizer on workability was the polycarboxylate ether-based superplasticizer (PCE). For example, when the optimum dose, corresponding to the highest strength, was slightly exceeded, there was a possibility of a sharp drop in strength, even if the segregation was not noticeable. At construction sites, however, the workability adjustment is required to control the slump loss. The question here is how sensitive are different fine cement mixtures that are differently blended with fine additions, like silica fume, to a small increment of this superplasticizer at different water content. In this study, this sensitivity was studied throughout four series of different fine mixtures. For each series, two water to cement ratios (w/c) were used, 0.35, and 0.45, while the superplasticizer dose, the superplasticizer to cement ratio, was varied from 0.011 to 0.0132 (g/g) for each (w/c) ratio. It was found that the small PCE increment caused strength improvement for some mixtures, while it caused strength reduction for others. When the content of both sand and silica fume were reduced, the small increment, along with increasing (w/c) ratio, could significantly decrease the strength by 7.5 MPa. Accordingly, it was concluded that the effect of the dose increment could be related to the actual water content rather than the (w/c) ratio. Hence, an indicator of the actual water content was proposed, which was useful to define a safe method for workability adjustment.

Behaviour of sustainable high strength self-compacting concrete with electrically precipitated fly Ash(EPFA) – A thermal waste

Concrete is the most common heterogeneous material in the construction industry. Admixtures have gained wide use in modern constructions with congested reinforcement with ambitious casting conditions. For such applications, self-compacting concrete (SCC) is the only special concrete with high cohesiveness and fluidity. This paper shows the study on the fresh properties, compressive, flexural, and split tensile strength, and RCPT, sorptivity of SCC with partially replaced electrically precipitated fly ash (EPFA) from 0 to 30% at 5% interval in cement and polycarboxylate ether-based superplasticizer as a chemical admixture. Compared the results with conventional SCC mix the fresh concrete performance was studied through the measurement of passing ability, filling ability and flowing ability by using L-Box, U-Box, V-Funnel and slump flow. The microstructure of the concrete was analysed with the help of a Scanning Electron Microscope(SEM) and X-Ray Diffraction(XRD). The results showed that 20% EPFA as partial replacement to SCC gives better results than the conventional concrete, thereby leading to economic profits as well as ecological benefits.

Temperature effect on compressive strength and quality grading of standard grade concrete with partial replacement of natural coarse aggregate by burnt wood pellet aggregate

This research work aims to experimentally investigate the effect of temperature on the standard concrete grade of M50 with partial replacement of natural coarse aggregate by burnt wood pellet aggregate. Concrete with and without burnt wood pellet coarse aggregate was exposed to a temperature of 250℃ for 24 h after 28 days of normal curing. Partial replacement of natural coarse aggregate with burnt wood pellet aggregate was considered having varying percentages 15, 30, 45, and 60% by weight without altering the w/c ratio and dose of polycarboxylate ether-based superplasticizer. Thirty standard cylindrical specimens of size 150 mm diameter and 300 mm length for control concrete and concrete with different replacement levels of burnt wood pellet coarse aggregate were cast to study the response of this concrete in normal as well as exposed to a temperature of 250℃ in terms of strength and its quality grading. The results show that the compressive strength of concrete decreases significantly with increasing burnt wood pellet aggregate. The decrement in compressive strength incorporating burnt wood pellet aggregate is found more significant at the considered temperature than in normal conditions. However, energy dissipation after attaining the peak load increases with an increase in percentage replacement of burnt wood pellet aggregate. The concrete with 60% replacement level under ordinary condition, the quality grading of the concrete was good while with lower replacement levels it was excellent. Upon exposure to temperature, quality grading of the concretes with the lower replacement levels goes down to good however, for the concrete with a 60% replacement level it remains unaffected.

Further insight into the strength development of cemented paste backfill materials containing polycarboxylate ether-based superplasticizer

The utilization of water-reducing admixtures has become immensely popular in underground mine backfilling operations not only to enhance the workability of cemented paste backfill (CPB, a mine construction material), but also for their ability to enhance the mechanical strength and long-term durability of CPB. This study aims to evaluate the effect of a polycarboxylate ether-based superplasticizer (PES) on the mechanical strength of CPB made with different mix components (tailings, dosages of PES, cement and solids contents, tailings fineness, and water chemistry), and subjected to various curing conditions (stress-free, under stress, constant temperature, and non-isothermal temperatures). An extensive experimental program has been conducted to investigate the uniaxial compressive strength development, hydraulic (positive pore pressure, suction) and microstructural properties of CPB with PES. The results show that including PES in CPB mixtures significantly increases the unconfined compressive strength (UCS) as well as affects the microstructure and hydraulic properties of CPB. This UCS increase depends on the amount of PES added, type and fineness of the tailings, sulphate content, and curing time. After 7 days of curing, the UCS of the CPB increases as the dosage of the PES is increased. The CPB that contain PES and cured under stress exhibit a higher compressive strength after just 3 days of curing as compared to that without PES and cured under similar stress conditions. It is also found that curing CPB under non-isothermal conditions considerably increases the compressive strength and this increase is more significant with the presence of PES. These findings have significant impacts on the short- and long-term performances of CPB structures with PES and their associated economic implications for underground mine backfilling operations.

Effect of polycarboxylate ether-based superplasticizer dosage on fresh and hardened properties of cement concrete

Ready-mix concrete nowadays is available almost everywhere in the country. RMC plants are indispensably using high-range water-reducing admixtures namely, sulfonate naphthalene formaldehyde condensate, and Polyether polycarboxylate, for making standard cement concrete. These admixtures are used to economize the cost of concrete by reducing the quantity of water. Commonly used high range water reducer admixture, the polycarboxylate ether-based (PCE) superplasticizer has been used to investigate its influence on workability and strength of concrete by measuring slump and ultrasonic pulse velocity as well as crushing strength. The cement of grade 43 has been used in this work. This superplasticizer was added to the mix to make concrete of grade M60 by weight of cement with 0.15%, 0.25%, 0.35%, 0.45%, and 0.55% without altering the w/c ratio. Experimental results reveal that the restricted dosage of the superplasticizer provided in Plain and reinforced concrete code of practice in Indian standard, IS456:2000, restricts to 1% is on the higher side. The slump, ultrasonic pulse velocity, and crushing strength of M60 grade standard concrete with water to binder ratio of 0.40 gives the optimum dose 0.45% by weight of cement, which is quite less than the restricted quantity of dosage.

Characterization of sewage sludge incineration ashes from multi-cyclones and baghouse dust filters as possible cement substitutes.

Incineration is not a final disposal method for sludge management since a significant amount of ash is generated. Although some published literature reported on the use of sewage sludge ashes (SSAs) as a cement replacement, none of them referred to the air pollution control unit of the incinerator where the SSA is collected. The properties of SSAs from different air pollution control units were investigated with the purpose of usage as a cement replacement in the present study. The SSA samples obtained from multi-cyclone units (MC-SSA), where SSA is collected at the bottom of the unit with the help of inertia and centrifugal forces, and baghouse dust filters (BHD-SSA), where SSA is collected at the fabrics of the unit, of the sludge incinerator were analyzed for chemical and physical characteristics, including heavy metal leaching, mineralogy (XRD), and particle morphology (scanning electron microscopy). Mortar samples were prepared with 15 and 30% of MC-SSA and BHD-SSA additions and analyzed for workability, strength activity, strength development, and freeze-thaw resistance. Heavy metal leaching results of both of the MC-SSA and BHD-SSA and their mortars were below the legal requirements of landfills, inferring that the toxic elements in SSA would not be of environmental concern in case SSA is used in cement matrices. The present study identified the variability of the physical and chemical properties of both SSAs over time and their differences. Incompliances of the SSAs to the pozzolanic material standards were observed, although moderate pozzolanic activity was concluded. In order to obtain the required flow value, different amounts of polycarboxylate ether-based superplasticizer were used in all of the mixtures. The levels of amorphous phases were found to be 23.3 and 39.3% for MC-SSA and BHD-SSA, respectively. MC-SSA exhibited less porosity with larger agglomerates than BHD-SSA. Ninety-day compressive strength levels of MC-SSA mortars with 15% replacement, which was found as 50.53 MPa, was higher than that of BHD-SSA mortars by 6% (47.65 MPa). The freeze-thaw resistance and water adsorption capacity of SSA mortars were comparable with that of the cement mortars. It was inferred that the contribution of SSA substitution to the strength development was influenced by hydraulic activity more than pozzolanic activity.Graphical abstract.

Strength development of cemented tailings materials containing polycarboxylate ether-based superplasticizer: experimental results on the effect of time and temperature

Superplasticizers are widely used in the backfill industry for the improvement of the flow ability of cemented paste backfill (CPB) while keeping water content low. However, the coupled effects of temperature and curing time on the mechanical strength of CPB with superplasticizers are poorly understood. This paper presents new findings of research conducted to experimentally assess the effects of a polycarboxylate-based superplasticizer on the strength of CPB subjected to varying curing time (1, 3, 7, and 28 days) and temperature (2 °C, 20 °C, and 35 °C). The binders used were Portland cement type I, fly ash, and blast furnace slag. Superplasticizer contents of 0, 0.125, and 0.25 percent of the total weight of the CPB were added. Various microstructural analyses and monitoring programs were also conducted to understand the principles behind the patterns in the strength of different CPB samples. The results obtained show that the unconfined compressive strength (UCS) of the CPB containing polycarboxylate-based superplasticizer increases with time. Moreover, the increase in superplasticizer content was observed to improve the UCS of the CPB (0.25% > 0.125% > 0%). The temperature was also observed to play an important role in strength development as the UCS increases with the rise in the curing temperature for all samples. It is also found that the temperature-induced strength increase is more significant for the CPBs that contain the superplasticizer than for those without superplasticizer. It was also observed that the CPB containing superplasticizer maintained a relatively similar strength upon replacing the cement with 50% slag while showing a sharp decline with fly ash. The findings from this study will be useful towards a cost-effective design of backfill structures.

Electrical indication of binary cementitious materials with steel fibres ability to resist the low permeability of concrete

The main objective of this study is to identify the durability properties of the test method, chloride ion penetration and sorptivity test in the combination of waste binding materials (supplementary cementitious materials) along with steel fibre reinforced concrete for various mixes. Most of the prediction methods, how much chloride ion ingress into the concrete and water absorption are mainly related to the long term serviceability of the deterioration of concrete. This laboratory experimental test results for 28, 56, 90 days for the RCPT values 31.54%, 34.26% and 38.16% respectively and 40.68% and 17.98% for 56 and 90 days test results for water absorption based on the test results has striving to produce the better improvement of structural concrete when the addition of slag up to 20% with low calcium fly ash up to 20% along with 1.5% of steel fibres and also addition of RHD up to 9.4 L for 470 kg/m3 of cement (binding materials) along with 1.5% of polycarboxylate ether-based superplasticizer with low w/b ratio of 0.32.

Ultrasonic and superplasticizer assisted dispersion of hybrid carbon nanomaterials (FCNT and GO): its effect on early stage hydration and physico-mechanical strength of cement mortar

In the present study, the prominent role of carbon nanomaterials (GO or FCNTs) individually and hybrid carbon nanomaterials (Hybrid-CNMs) on early stage of hydration of ordinary Portland cement has been investigated. Hydration rates were quite dominant in case of hybrid CNM-CNCs as compared to CNM-CNCs due to additional nucleation sites as well as interfacial adhesion provided by the 3-D hybrid framework of Hybrid-CNMs. Further, hydration rate was found to be prevalent in case of Hybrid-CNMs without use of polycarboxylate ether based superplasticizer (PCE-SP) at earlier hydration ages (i.e. up to 24 h), while it was predominant in case of Hybrid-CNMs with use of PCE-SP at later hydration ages of 48 h as shown by XRD and TGA studies. Compressive strength and split tensile strength were enhanced by 83.6% and 52.7% for SP@Hybrid-CNM as compared to control sample at 28 days of hydration as a result of additional production of hydration products (C–S–H) at the composite’s interface. TGA results revealed that sample incorporating Hybrid-CNMs produced higher quantity of calcium hydroxide.

Positive synergistic effect of superplasticizer stabilized graphene oxide and functionalized carbon nanotubes as a 3-D hybrid reinforcing phase on the mechanical properties and pore structure refinement of cement nanocomposites

The current investigation presents the superior mechanical performance of polycarboxylate ether based superplasticizer (PCE-SP) stabilized hybrid carbon nano-materials (HCNs) over individual GO (graphene oxide) or FCNTs (functionalized carbon nanotubes) as reinforcing agent in the cement nanocomposites (CNCs). Superplasticizer (SP) stabilized nanomaterials (SP-GO, SP-FCNT and HCNs) exhibit a good dispersion behavior in aqueous as well as alkaline environment of cement pore solution. The increased dispersion of HCNs due to SP steric stabilization as compared to GO or FCNTs has been monitored by UV–Visible spectroscopy. The compressive strength enhancement for HCN-CNCs (at 0.02% loadings by weight percentage of cement) was found to be 43.08% which was superior to strength improvements of 27.39% and 17.82% by GO (0.02%) and FCNTs (0.08%), respectively, in comparison to control at 90 days of curing. On the other hand, split tensile strength for HCNs incorporated mortar was found to be 52.20% at dosage of 0.08%. While, GO-CNCs and FCNT-CNCs showed a maximum improvement in tensile strength by 37.97% and 37.21% at loadings of 0.04% (bwoc) at curing age of 90 days. The improved degree of hydration of silicates in case of HCN-CNCs has been shown by appearance of flower-shaped regular hydration patterns and better quantity of hydration products formation as compared to control sample as observed by FE-SEM (field emission-scanning electron microscope) and XRD (X-ray diffraction) studies, respectively. In addition to this, Mercury Intrusion Porosimetry (MIP) studies showed reduction in porosity by 25.2%, 31.0% and 46.5% for FCNT-CNCs, GO-CNCs and HCN-CNCs respectively, in comparison to control.

Admixtures Used in Self-Compacting Concrete: A Review

Self-compacting concrete or self-consolidated concrete is a highly flowable, non-segregating concrete which spreads into congested reinforcement area and fills the formwork without the use of any vibrators. Self-compacting concrete allows denser reinforcement, optimized concrete section and shapes, and greater degree of freedom. It has the advantages of maintaining the durability and characteristics and meeting expected performance requirements. It has been used ideally in bridges, drilled shaft, and earth-retaining structure, columns and area with high concentration of rebars and pipes. The self-compacting concrete improves constructability, reduces skilled labor and noise level, minimizes the voids in highly reinforced area, gives superior strength and durability and smooth and uniform surface finishing and accelerates the project schedules. In the present study, various mineral admixtures, i.e., ground-granulated blast-furnace slag, limestone powder, silica fume, fly ash and chemical admixtures such as sulfonated melamine formaldehyde condensate, melamine formaldehyde, sulfonated naphthalene formaldehyde condensates and polycarboxylate ether-based superplasticizer, have been studied in the self-compacting concrete. A critical review of the effect of combination of these mineral and chemical admixtures on various rheological, strength and durability properties of the self-compacting concrete is presented in this paper.