Superplasticizer Research Articles

Predicting compressive strength of geopolymer concrete using machine learning

The anaconda software required python code in order to run the utilized individual K-nearest neighbor (KNN), random forest regression (RFR), and linear regression (LR) models. The results show that RFR machine learning (ML) technique out of the other utilized models shows the best performance for a used dataset. The findings of this article indicate that the dataset utilized proposed model provides an acceptable algorithm for FACC design and optimization. In the current study of preparation of geopolymer concrete (GPC), relevant variables such as curing, fly ash, calcined clay, added water, super plasticizer, coarse aggregate, quarry stone dust, caustic soda, and water glass were used as input parameters. The ranges, mode, median, standard deviation, and other identifying details were checked using descriptive statistical analysis for the input parameters. The strength due to the compression of FACC GPC was predicted using RFR, LR, and KNN ML techniques, all based on Python coding. The ensemble ML technique, RFR outperformed the individual ML technique, KNN, in terms of prediction. The RFR indicates that the maximum amount of [Formula: see text] is 0.92, and LR provides 0.58, although the KNN was less accurate, with a coefficient of determination of 0.56. The RFR technique’s lower values of errors, mean absolute error (MAE), MSE, and root mean square error (RMSE) yield 1.99, 7.17, and 2.67[Formula: see text]MPa, respectively. The excellent accuracy of the RFR methodology is confirmed by a statistical analysis of errors. Curing temperature, curing hours, molarity of NaOH, and FACC ratio significantly affect the compressive strength (CS) of FACC GPC. The findings indicate that the proposed model provides an acceptable algorithm for FACC design and optimization using RFR among the three combinations of ML methods for a given dataset.

Investigation of Mechanical Properties of M-sand concrete with Polypropylene and Steel fibers

This study looks into the impact of the adding of polypropylene(pp) and Hooked-end steel (HES) fibre on the mechanical characteristics of M-sand concrete (MSC). HES fibres with a 30-mm length were used at 1% to the weight of the cement for every mix and Polypropylene(pp) fibers with length 12-mm were used at the content of 0.25%, 0.50%, and 0.75% and 1%. All the mixes were produced with the mixing of HES and pp fibers. All the mixes with fiber-reinforced concretes (FRC) contained 60% M-sand as fine aggregate (FA) replacement. For increment of workability, the super plasticizer is also added. The compressive strength, splitting tensile strength, flexural strength of the concrete mixes was examined for M30 Concrete. Results of this work indicated that the adding of the M-sand improves compression characteristics of plain concrete mix. The outcomes also show that the mechanical characteristics of MSC were amplified by the addition of steel (HES) and polypropylene (pp) fibers at each weight fraction taken into account in this investigation. Additionally, it was found that adding 1% steel fiber considerably increased the concrete’s split tensile test values and also flexural test values. The blend with the highest performance out of all the varied steel and polypropylene(pp) fibre combinations tested had 1% HES and 0.5% pp fiber. Finally, the findings demonstrated that adding fibres to concrete led to reduction in compressive strength and increase in the value of split tensile strength and also flexural strength.

Effect of polypropylene fiber on workability and strength of fly ash-based geopolymer mortar

Geopolymers do not require Portland cement as a binder; hence, the binder is replaced by a material containing high SiO2 and Al2O3 reacted with an alkaline activator (NaOH and Na2SiO3). In addition, mortar or concrete is highly susceptible to cracking, requiring the addition of polypropylene fiber (PPF). This research belongs to an experimental study examining the addition of PPF with percentages from 0%, 0.25%, 0.5%, 0.75%, and 1% by utilizing coal fly ash (FA) as a precursor. This study also added a superplasticizer (SP) and extra water (EW) to maintain the flowability. The tests were carried out on the workability, strengths, and microstructure of geopolymer mortar. Workability obtained values of 140 - 220 mm. Furthermore, the highest compressive strength of 73.3 MPa and flexural strength of 9.92 MPa were identified in the geopolymer mortar with the addition of 0.5% PPF. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) tests were applied to investigate the geopolymer microstructure.

Properties of concrete using waste iron

Iron filings are considered waste products produced from metalworking processes as small pieces of iron that look like fine powder. In this research, the landfill is the method of dealing with this waste. In the current investigation, iron filings have been employed to determine their appropriateness as afine aggregate in concrete production. Replacing all or a portion of the fine aggregates with iron filings would result in significant environmental benefits. The replacement percentages of fine aggregate by IR are 0 %, 10 %, 20 %, 30 %, and 40 %. The water cement ratio adopted in this work is 0.58. The experimental investigations in the fresh state show that the slump of the mixtures containing 10 %–40 % of iron filings (IR) varied from 71 to 76 mm. The results showed a decrease in the slump of up to 16.47 % for the mixtures containing different percentages of IR compared to the reference mixture. This decrease is evident in mixtures containing IR ratios between 20 % and 40 %. However, the superplasticizer (SP) addition improved each slump and compaction factor. The compressive strength of the mixtures containing 10 %–40 % was within the range of (28.21 to 40.44) MPa at 28 days. The flexural strength was within the range (of 4.51 to 6.51) MPa at 28 days. According to the results of this study, the addition of IR decreased the compressive strength and flexural strength by up to 38.51 % and 44.32 percent at the age of 28 days, respectively. The importance of the study comes from the attempt to reuse waste iron filings as fine aggregate to save sources of our environment and contribute to the sustainable concrete industry.

The Role of Granite Waste Powder on Mechanical and Durability performance of GGBS and Metakaoline based concrete

Industrial wastes such as granite waste powder (GWP), GGBS, and Metakaoline (MK) are widely available in numerous Indian states. Due to their pozzolanic abilities, GGBS and Metakaoline were used as a partial alternative to cement in the manufacture of concrete, with constant levels of 40% GGBS and 10% Metakaoline. In addition, to minimize the use of natural resources, granite waste was used as a fine aggregate substitute in various percentages (0, 10%, 20%, 30%, and 40%) on a weight basis, and a PC-300 Maximo-Plats super plasticizer with a dose of 0.3 percent was used to retain the essential workability. For this project, M45 grade concrete with a w/c ratio of 0.36 was used to assess the mechanical properties of blended concrete at the ages of 7 and 28 days. At 28 days of age, durability studies such as water absorption and RCPT tests were conducted. According to the experimental data, the optimum compressive strength of blended concrete was found to be at a 20% replacement of GWP.

Quantify the Physical Properties of Concrete by Partial Replacement of River Sand by M- Sand Using Fly Ash as Mineral Admixture

Abstract: Sand and cement, which go into making concrete, is in great demand because it is a crucial building material. Due to this demand, environmental degradation is rising during the production of cement and river basins are running out of sand. Concrete is being updated with suitable substitutes without sacrificing its durability and strength. Fly ash and M sand are used in this study as alternatives to cement and fine aggregates, respectively. Fly ash is by product of combustion process; hence utilizing this product in concrete can be advantageous to both the environment and cost considerations. Whereas M sand is obtained by crushing aggregates into desirable sizes which can benefit workability of concrete .The percentage of these alternatives for which partial replacement results in higher test values is indicated in this study. Super plasticizer was used in testing on newly laid concrete. M 45 grade concrete mix design as per IS 10262:2019 is calculated. Testing was done on M45 grade fresh concrete for workability: slump cone test, compaction factor test, vee bee consist-meter test, as well as hardened concrete for compression strength, tensile strength, and flexural strength. The tests were conducted for variable percentages of fly ash and M sand by weight of cement and natural sand replacement. In this study natural sand is replaced with M sand in 0, 10, 20, 30, 40 & 50% for every 0%, 10% & 15% replacement of fly ash with cement. Satisfying results were found for 10% fly ash and 40% M sand mix for both workability tests and strength tests conducted in the specimen.

Compressive and Impact Loads' Effects on The Behaviour of SIFCON Made of Plastic Waste Fibers

SIFCON is a relatively new material and consists of slurry (cement or cement and sand), water, super plasticizers (water reducers) and fibers. In all previous research, steel fibers and other types of fibers were used, but in this study, waste plastic fibers Polyethylene Terephthalate (PET) created by cutting carbonated beverage bottles were used for the first time in the production of SIFCON. Three volume ratios (3%, 6% and 10%) of the total volume of the concrete mixture were used to add fibers in different volume ratios, and a reference concrete mixture was created for comparison. Tests of compressive strength, impact resistance, ultrasound transmission velocity check and other tests were performed on the constructed models. Compared with the reference concrete, according to the analysis of the results. The results showed an improvement in the compressive strength it increased by (18.5%), an increase in the impact resistance by (416.67%), and a decrease in the velocity of ultrasound by (19.42%).

Using mixture design method for developing and optimizing eco-friendly ultra-high performance concrete characteristics

Due to its high cement content, ultra-high performance concrete (UHPC) is not an eco-friendly material. Utilizing alternative materials as a replacement of cement could improve UHPC's sustainability and reduce environmental impact. This study intends to examine the impact of using different alternative filler materials such as quartz powder (QP), limestone powder (LP), granite powder (GP) and basalt powder (BP) along with silica fume (SF) as a cement replacement on mechanical characteristics and durability of UHPC. The total powder content composed of 60% cement, 20% SF, and 20% filler materials (QP, LP, GP, and BP). Mixture design method in Minitab program was used to design concrete mixtures. Flowability, compressive strength, water permeability, rapid chloride permeability, sulfate resistance and concrete microstructure were the tests performed on the concrete mixtures. Utilizing QP, LP, BP, and GP as a partial replacement of cement in the production of UHPC resulted in significant negative impact on concrete flowability. UHPC with low environmental impact and compressive strength more than 120 MPa with higher durability could be produced using QP, LP, BP, and GP as a replacement of cement. Mixture composed of 711 kg/m3 cement, 237 kg/m3 SF, 118.5 kg/m3 QP, 118.5 kg/m3 BP, 1017 kg/m3 sand, 142.2 kg/m3 water, 31.3 kg/m3 super plasticizer, and 156 kg/m3 steel fibers achieved the highest compressive strength at age 7, 90, 180 days, the strength were 85 MPa, 123 MPa, and 126.1 MPa respectively. The findings demonstrated the development of a strong relationship between responses and constituent materials in predicting and optimizing compressive strength of UHPC, enabling construction implementers to obtain mixture design proportion to obtain UHPC with certain desirable properties using the proposed models without resorting to making experimental mixtures using a trial-and-error method, which consume time and effort.

A comparison of stress-strain behaviour of conventional and high strength concrete

Strength performance of concrete is characterized by its compressive strength, elastic modulus, stiffness and energy absorption capacity. Stress strain behaviour of concrete encompasses information on all these parameters, and is thus one of the most vital data to assess its overall performance. The present study utilizes the stress strain response, as a tool, to compare the relative variation in performance of conventional and high strength concrete. Two set of mix compositions (viz., M40 and M80 grade concrete) have been designed. The designed compositions are checked for their target strength by performing load controlled tests on 28 day cured cube specimens. M40 grade concrete comprises of cement and water as binding material, and fine and coarse aggregates as filler. High strength concrete (M80 grade) is designed with cement, mineral admixture and water as binding material; while the fine and coarse aggregates contribute to the filler material. For high strength concrete, super plasticizer has been added in required proportion to ensure adequate workability. Displacement control tests, with controlled strain rate, have been performed on 28 day cured cube specimens. Variability in pre-peak and post-peak stress strain response is analysed for both conventional and high strength concrete. An average of response over atleast four samples is computed for both the M40 and M80 grade concrete. In present study, the characteristic response is normalized with respect to peak strength to obtain a common reference basis and compared. The comparison is summarized in terms of change in pre-peak response and post-peak ductility. The observed results enable quantification of relative change in performance for M40 and M80 grade of concrete. The results are significant for benchmarking performance of high strength concrete structures with those of conventional concrete structures.

Experimental study on the slump-flow underwater for anti-washout concrete

The workability of underwater anti-washout concrete (UWC), especially the flowability in particular application environments, was always a critical and controversial issue. In this paper, a new test device and approach have been proposed to study the behavior of underwater flowability of UWC and establish a relationship with laboratory slump-flow tests. Further, the effects of different mix proportions, such as aggregates, superplasticizer (SP), water-cement ratio (W/C), anti-washout agents (AWAs) type and dosage, beside yield stress and plastic viscosity of UWC were investigated. The differences (Δd) between the spread diameter of the samples in air and underwater were compared. The results indicate that the flowability of concrete underwater is less than that in air, and it was proved that there is significant association between the yield stress and Δd. Also, various factors that affect the spread diameter difference are prioritized to optimize the rheological properties and limit the underwater flowability loss as much as possible. Combined with the Roussel's flow model and stress equilibrium differential equations, the theoretical formula of interpreting UWC's underwater flowability loss by yield stress was deduced, which can certify that the buoyancy underwater counteracts part of the gravity that keeps the UWC flowing freely and reduces its maneuverability. Additionally, an empirical formula of underwater spread diameter of UWC was proposed according to the variation law that the spread diameter difference decreases due to the increase of yield stress. Finally, the outcomes provided basic theoretical reference to filling capacity of UWC when casting underwater.

Effect of additional water or superplasticizer on key characteristics of cement paste made with superabsorbent polymer and other shrinkage mitigating materials

The use of superabsorbent polymer (SAP) coupled with expansive agent (EA) or shrinkage-reducing admixture (SRA) can effectively reduce shrinkage of cement-based materials. However, SAP particles at high contents can adversely affect rheological and mechanical properties. Securing proper workability can be accomplished by additional water or adjusting the superplasticizer (SP) demand. There is an uncertainty about the efficiency of these approaches to workability compensation. This study evaluates the effect of additional water or SP on key properties of cement paste made with SAP and relatively high content of EA or SRA. Macro and micro mechanisms underlying the effect of combined shrinkage mitigating strategies on the performance of cement paste made with 0.4 water-cementitious materials ratio are investigated. Results indicate higher efficiency of increasing SP demand by 0.6% versus the addition of water by 30 g per gram of SAP. Up to 80% higher compressive strength is obtained for the mixtures made with additional SP, which is attributed to up to 33% reduction in capillary porosity and smaller pore-size distribution of the hydrated cement paste. In the presence of high EA content, the use of additional SP prevents excessive initial expansion in the paste with additional water.

Analysis and prediction of the effect of Nanosilica on the compressive strength of concrete with different mix proportions and specimen sizes using various numerical approaches

AbstractIntroducing nanotechnology in concrete is one of the most significant successes in enhancing the mechanical properties of concrete. It affects the quality of the microstructure of the concrete due to its extremely small nanoparticles leading to a faster reaction due to its large surface area. The nanoparticles fill the concrete's pores, resulting in considerably improved strengths in the early ages of the concrete. This research used six models; linear regression (LR), multilinear regression (MLR), nonlinear regression (NLR), pure quadratic (PQ), interaction (IA), and full quadratic (FQ), to predict the compressive strength of the concrete modified with different Nanosilica contents for various mix proportions. The models were applied to three datasets, with 420 collected from several research studies. The ranges of the concrete mix proportions used in this study were as follows, water/cement ratio (w/c) ranged between 0.1 and 1, cement content (C) ranged between 153.81 and 1200 kg/m3, fine aggregate content (FA) ranged between 492 and 2270 kg/m3, coarse aggregate content (CA) ranged between 617 and 2900 kg/m3, superplasticizer (SP) ranged between 0% and 6.7%, coarse aggregate size (CAS) ranged between 6 and 50.8 mm, fine aggregate size (FAS) ranged between 0.025 and 10 mm, Nanosilica content (NS%) ranged between 0% and 15%, w/c of 0.4–0.6 and the curing time (days) ranged between 3 and 180. The compressive strength of the collected datasets ranged from 3 to 120 MPa. The parameters that have improved the analyzed datasets of the compressive strength were the content of Nanosilica and the SP. The models were assessed for their accuracy using multiple assessment criteria; the most evident ones are; the objective function (OBJ), root mean square error (RMSE), Scatter Index (SI), and the maximum absolute error (MAE). The analytical models and the model comparison operations will be shown in detail in this research, indicating that the most effective and accurate model is the FQ model; where coefficient of determination (R2) of 0.96, RMSE of 3.49 MPa, MAE of 2.96 MPa, and SI of 0.08 were conducted from the analytical studies. From the developed models, the compressive strength of the concrete up to a high compressive strength level with high accurately can be predicted. Also, the compressive strength of the concrete can be accurately predicted for various sizes of aggregate and specimens.

Homogeneous flow performance of steel-fiber reinforced self-consolidating concrete for repair application: A biphasic approach

In this study, fiber-reinforced self-consolidating concrete (FR-SCC) was considered as a diphasic suspension of fiber and coarse aggregate (F-A ≥ 5 mm) skeleton in mortar suspension with solid particles finer than 5 mm. The coupled effect of the volumetric content of fibers, coarse aggregate particle-size distribution, and rheological properties of the mortar on the passing ability and dynamic stability of various FR-SCC mixtures was investigated. Nine high-strength and 10 conventional-strength FR-SCC mixtures for repair application were proportioned with water-to-binder ratios (W/B) of 0.35 and 0.42, respectively, and macro steel fibers of 0.1%–0.5% volumetric contents. The dosages of high-range water-reducer (HRWR) admixture were optimized to achieve a targeted slump flow of 680 ± 20 mm. The yield stress and plastic viscosity of the mortar mixtures varied between 4.6-17.7 Pa and 2.8–8.2 Pa s, respectively. Flow performance of the investigated mixtures were evaluated in terms of flowability (slump-flow test), passing ability (J-Ring and L-Box set-ups), and dynamic stability (T-Box test). According to the established correlations, the main influencing parameters on homogeneous performance of FR-SCC include W/B, paste volume, volumetric content-to-packing density of F-A (φ/φmax), HRWR dosage, fiber content, mortar rheology, and volume of excess mortar. The robustness analyses results revealed that homogeneous flow performance of FR-SCC is more sensitive due to variations of the φ/φmax and paste volume rather than mortar rheology, W/B, and HRWR dosage. The characteristics of the mixture constituents for FR-SCC mixtures with different strength levels were finally recommended to ensure acceptable homogeneous performance under restricted flow conditions of repair application.

Effect of water to binder ratio, polycarboxylate superplasticizer and metakaolin dosages on rheological and viscoelastic properties of fresh metakaolin-air lime pastes

As an ancient architectural restoration material, hydraulic lime has good early properties, which is necessary to ensure its successful application. Metakaolin-air lime (MK-AL) composite material as a kind of hydraulic lime, the initial fluidity, macroscopic rheological properties, viscoelasticity and dissolution-early hydration are systematically investigated by setting different water to binder (w/b) ratios, polycarboxylate superplasticizer (SP) and metakaolin dosages. The results showed that the initial fluidity of MK-AL pastes has a more obvious improvement by adding SP. The rheological behavior of MK-AL paste was well characterized by both the Bingham model and H–B model. The reduction of yield stress and plastic viscosity on account of the better dispersion of particles in MK-AL paste. The rheological behavior expresses shear thickening without SP and shear thinning with SP in MK-AL paste are revealed. The viscoelastic transformation is illustrated by the macroscopic viscosity index, elastic index, storage modulus, loss modulus, solid-liquid balance and fluidity index parameters, these parameters have a reduction to a large degree with increasing w/b ratios and SP dosage, while the variation of metakaolin dosage has relatively little impact. The increase in w/b ratio and SP dosage promote the dispersion and dissolution of the particles in the aqueous solution, and the strong dispersive capacity delays the process that particles heap up rapidly and network structure formation in MK-AL pastes. Furthermore, the exothermic rate of the two hydration stages is reduced significantly, as well as the appearance of the exothermic peak of hydration is delayed.

Designing Self-Compacting Concrete Using Local Materials from the Arid Region of Adrar, Algeria

Abstract In the construction sector, the non-renewable world resource of sand is largely used to produce mortar and concrete. It has been estimated that over 10 billion tons of sand have been produced, with 1.2 billion tons used in concrete over the last decade, which leads to a progressive reduction of available construction materials and environmental impacts. Since desert sand resources are abundant in arid region of Adrar (Southern Algeria), it would be viable to use desert-sand as an alternative material for the production of self-compacting concrete. Therefore, self-compacting concrete is experiencing significant demand in that arid region since it offers socio-technical and economic solutions to stakeholders in the construction and public works industry. Furthermore, the present study aims to address the concerns of these stakeholders. The results obtained showed that the self-compacting concrete that was made with local materials, behave correctly, both in the fresh and hardened states. This concrete included a 1% super plasticizer dosage, a gravel-to-sand (G/S) ratio varying between 0.8 and 1.1, and additions of limestone fillers up to 50% relative to the mass of cement for self-compacting concrete made with dune sand, while this percentage could go up to 38% for self-compacting concrete made with corrected sand (63% crushed sand with 37% dune sand).

Experimental Investigation on Mechanical Properties of Engineered Cementitious Composites

The hybridization cycle is utilized in this review to increment mechanical properties of Engineered Cementitious Composite (ECC). Two kinds of blend extents are utilized in this examination, in blend 1 mono fibre and blend 2 half breed strands. Then the various techniques utilized for oneself recuperating of cementitious materials, for example the utilization of empty strands, microencapsulation, broad specialists and mineral admixtures, microorganisms and shape memory are summed up. Designed Cementitious Composite (ECC) is another sort of concrete-based materials, which has interesting properties contrasted and customary cementitious materials. Further, a rundown about the examination status of self-mending on ECC is given. This paper presents the Compressive and rigidity of Engineered Cementitious Composites or additionally called as bendable cement under adding various sorts of mineral admixtures like (GGBS), and fly debris class F (FA). Specifically examined by adding PVA and PP (polypropylene) strands and conplast 430 high reach water diminishing specialist. It shows that ECC bears extraordinary potential in acknowledging viable self-recuperating because of its exceptional miniature break conduct and tight break width control property joined with its generally high level of cementitious parts and low water-folio proportion. In the wake of leading the different tests on blend extents, it is presumed that, finally the PVA and PP filaments were utilized in blend extents, the uniaxial compressive strength and direct rigidity are giving best outcomes and 1.12% of super plasticizer added to it, then the functionality is likewise expanded by looking at this multitude of two tests, and the ECC giving great outcomes than the traditional cement. The principal subject or point of this task is to give the pliable rigidity to the substantial and to stop the devastating disappointments of the designs.

Experimental and Analytical Investigation of R.C Beam with HPC Containing Nano Silica

Abstract: Concrete is the most widely used construction material in the world. It is a heterogeneous material composed of cement, fine aggregate, course aggregates and water. The proportion of these constituents affect the mechanical properties and durable properties of concrete. Also it is a versatile material due to the continuous demand. In recent years, lot of researches has been focused on improving the quality of concrete. This lead to the extension in the limitations to improve the performance of concrete with the addition of various admixtures super plasticizers subsidiary cementitious materials like silica fume, fly ash, blast furnace slag, metakaoiln, rice husk, etc. the properties like compressive strength, flexural strength, durability and workability of concrete enhances due to the addition of these materials. The concrete thus formed with high strength and durability compared to normal concrete are called High Performance Concrete. The compressive strength of HPC may be greater than 50Mpa. This HPC with compressive strength greater than 50Mpa can be used for structural members like beam, column, slab etc In this investigation the cement is replaced by 1%, 2% and 3% of Nano silica. Experimental and analytical investigation were done to investigating the flexural behaviour of conventional RC beam and R.C beam with HPC containing optimum percentage of Nano silica. Analytical investigation was done by ANSYS. This chapter discusses about the HPC, its mechanical strength properties like compressive strength, split tensile strength, flexural strength, effect of Nano materials like Nano Silica in HPC, determining the optimum percentage of Nano silica which gives maximum strength, investigating its durability property, investigating the strength development of RC beam with HPC containing optimum percentage of Nano silica, examining the load deflection behaviour of beam with HPC containing Nano silica and finally analysing the deflection of beam using Ansys. The key objective of this project is to investigate the importance of Nano silica as a replacement for cementitious materials in normal concrete and this paper presents strength and durable properties of HPC containing Nano silica.

Viscosity transition from dilute to concentrated cementitious suspensions: the effect of colloidal interactions and flocs percolation

The current paper deals with the effect of powder type and chemical admixtures on the rheological properties of mineral suspensions. The plastic viscosity of calcite, cement, and fly ash suspensions with or without superplasticizers (SP) and hydration retarders was characterized in a wide range of solid volume fractions. The results show that the plastic viscosity of suspensions increases with the decrease in particle size, and strongly decreases with the presence of superplasticizers. Besides, for reactive suspensions, hydration retarders decrease the plastic viscosity of the suspension, while competitive adsorption occurs when adding retarders to suspensions containing SP, leading to an increase in the plastic viscosity. Based on the experimental results, a relative plastic viscosity, i.e., the ratio between the total plastic viscosity and the theoretical viscosity contributed by the hard-sphere, is proposed to assess the effect of the contribution of colloidal forces. Moreover, the solid volume fraction of flocs in colloidal suspensions before percolation is identified by comparing the measured plastic viscosity with the Krieger-Dougherty model. Finally, a theoretical approach to determine the percolation packing fraction of minerals powders is further proposed.

Dilatancy swerve in superplasticized cement powder paste

Superplasticizer (SP), particularly poly-carboxylate based, can improve substantially the strength-workability limits of cement powder paste by decreasing the water demand for hydration. It however brings unfavourable effect of dilatancy which is the increased viscosity at high shear flow that impairs the pumpable distance and mixing uniformity. The dilatancy in cement powder paste was caused by the clustering of mobile and adsorbed polymers in SP that forms dead zone of flow and increase flow impedance. Previous research revealed that the dilatancy increased as SP dosage increased. Nevertheless, this study found that it does not increase monotonically as the SP dosage increases. It increases initially due to the introduction of SP but decreases after reaching the “critical SP dosage”. It is because adequate SP disperses effectively the cement particles for better hydration which decrease the interstitial void hence mobile SP polymers. This phenomenon is referred to “dilatancy swerve”, the understanding of which is essential in designing practical mortar or concrete mix to mitigate the impact of increased viscosity in pumping and mixing. To investigate the factors affecting the critical SP dosage, this study tested the dilatancy of various types of cement powder paste that consist of cement, fly ash (FA), silica fume (SF) and/or limestone (LS). It was found that the critical SP dosage decreased as FA was used to substitute an equal volume of cement but increased as SF or LS was used. Lastly, the general trend of decreasing dilatancy as WPD increased was observed.

Criticality of binder-aggregate interaction for buildability of 3D printed concrete containing limestone calcined clay

The study aims at understanding the criticality of interaction between the binder matrix and aggregate when a 3D printable mix is subjected to compression at an early age. Two binder systems containing fly ash and limestone calcined clay (LC2) as supplementary cementitious material are compared based on flowability and compression at an early age. The superplasticizer (SP) dosage for the mix with LC2 is observed to increase significantly to maintain equivalent flowability as the mix with fly ash. Compressive rheology (squeeze flow) test is performed at 5 and 30 min, and it is observed that the mix with LC2 shows an enormous growth in the compressive stress restraining capacity with time. Further, the effect of two types of aggregate, namely uniformly graded quartz sand (maximum size of 2 mm) and well-graded crushed stone sand (maximum size of 4.75 mm), on buildability is studied. It is observed that the total printed height of the hollow cylinder before collapse increases from 220 mm for quartz sand mix to 1.14 m for mix with crushed stone sand, possessing the same flowability. It is also observed that when the layers are subjected to compression due to printing, the rheological properties of the binder matrix are more critical within the first few minutes (5 min) of deposition, whereas the binder matrix-aggregate interaction becomes the influencing factor at later ages (30 min).