Mass Of Cementitious Materials Research Articles

Measuring the performance of CO2 injection into field-cured concrete in the Arabian Gulf climate: an experimental study

ABSTRACT Concrete has experienced significant improvements in recent decades, resulting in lower Portland cement consumption as well as a lower carbon footprint through CO2 injection while keeping comparable fresh, mechanical, and durability performance. The use of CO2 injection in concrete (CarbonCure) in the United States and Canada has enabled advances such as green concrete under normal and severe conditions. While incorporating novel developments, this study focuses on CarbonCure concrete modification in the extreme weather of the Arabian Gulf region. This is a relatively new option that has entered the field in the Middle East. The materials, process, and fresh and hardened properties of the CarbonCure concrete made and field cured in the Arabian Gulf region will be considered here and evaluated in detail. Along with adding CO2 to the mix, the cementitious material was lowered without impacting the quality or performance of the structural concrete. The developed green mix included up to 0.2% CO2 by mass of cementitious material. Because of the benefit of early carbonation, which strengthened the concrete product even with less cementitious material, this green concrete mix retained a 28% increase in slump compared to the standard concrete mix without CO2, a 28-day compressive strength of 48 MPa, low water absorption of 1.3%, and resistance to aggressive chemicals, all within the limits defined by the standard codes. Due to these benefits, and because this green concrete was tested against the severe coastal climate, it would be ideal for maritime applications.

Influence of calcium sulfate dihydrate as chemical activator on compressive strength of hardened fly ash-cement pastes

The present study focuses on evaluating influence of calcium sulfate dihydrate (CaSO4.2H2O) as a chemical activator on compressive strength of hardened pastes containing fly ash and cement as cementitious materials. A high amount of Class-F fly ash used to replace Portland cement ranged from 85 to 93% by mass of cementitious materials. For all the pastes, a low water-to-cementitious materials ratio of 0.20 was prepared. The amounts of CaSO4.2H2O added to the mixtures were 0.0, 1.5, 2.0, and 2.5% by mass of cementitious materials. Experimental results showed that at the age of 3 days, the compressive strength of hardened paste specimens using CaSO4.2H2O was higher 1.21–2.15 times than that of the control paste specimen without CaSO4.2H2O. At the age of 7 days, the compressive strength of hardened paste specimens using CaSO4.2H2O still continued to be higher 1.03–2.06 times than that of the control paste specimen without CaSO4.2H2O. At the ages of 14 and 28 days, the compressive strength of hardened paste specimens using CaSO4.2H2O was approximately equal to that of the control paste specimen without CaSO4.2H2O. Consequently, the addition of CaSO4.2H2O improved the early-age compressive strengths of the fly ash-cement pastes, and the CaSO4.2H2O content of 2.0% by mass of the cementitious materials was effective in increasing the compressive strength of such pastes.

Frost Resistance and Mechanism of Circulating Fluidized Bed Fly Ash-Blast Furnace Slag-Red Mud-Clinker Based Cementitious Materials.

The motivation of this work is to enhance the long-term frost resistance of circulating fluidized bed fly ash (CFA)-based multisolid waste cementitious material (CSM). In this research, CSM2 is prepared by 30 wt.% CFA, 20 wt.% blast furnace slag (BFS), 10 wt.% red mud (RM), 10 wt.% phosphorus slag (PS), and 30 wt.% cement clinker (CC). The strength and mass of CSM are detected by a press and electronic balance. The hydration products, polymerization degree, thermogravimetric, micromorphology, pore structure, and harmful element leaching are detected by XRD, MAS NMR, TG-DTG, SEM-EDX, MIP, and ICP-MS. The major findings indicate that the strength loss, mass loss, and strength of CSM2 after 25 freeze–thaw cycles (CSM2-25) are 2.35%, 0.36%, and 49.95 MPa, respectively, which is superior to other CSMs and still meets the performance requirements of fly ash Portland cement 42.5#. The main hydration products are C-S-H gel, C/N-A-S-H gel, and ettringite during the freeze–thaw cycle. The polymerization degree and thermogravimetric loss of hydration products in CSM2-25 are 50.65% and 12.82 wt.%, respectively, which are higher than those of other CSMs under the synergy of CFA, BFS, RM, and PS. In addition, the microscopic results show that the interface between the paste and aggregate, micromorphology, and pore structure of CSM2-25 are the densest when the mass ratio of Ca/(Si + Al) is 0.81. These characteristics are beneficial to the improvement of long-term frost resistance in CSM2. Finally, the leaching results of harmful elements in CSM2 after 25 freeze–thaw cycles still meet the WHO standard of drinking water. Therefore, this work provides a reliable reference for the preparation of green cementitious materials with great frost resistance by using CFA, BFS, RM, and PS.

The Synergistic Effect of Ester-Ether Copolymerization Thixo-Tropic Superplasticizer and Nano-Clay on the Buildability of 3D Printable Cementitious Materials.

The shape retention ability of materials deposited layer by layer is called buildability, which is an indispensable performance parameter for successful 3D printable cementitious materials (3DPC). This study investigated the synergistic effect of nano-clay (NC) and thixotropic superplasticizer (TP) on the buildability of 3DPC. The rheological parameters and static yield stress are characterized by the rheology testing, the green strength is measured by a self-made pressure tester, and the fluidity is tested by flow table. Results indicate that NC significantly increases the growth rate of static yield stress and green strength and TP can improve the initial rheological parameters and fluidity, which ensures the initial stiffness and workability of printed materials. The mixture with 7‰ (by mass of cementitious materials) NC and 3‰ TP obtains excellent extrudability and buildability, due to the synergistic effect of NC and TP. Based on the rheology testing and specific printing experiments, a printable window with 1.0 Pa/s~2.0 Pa/s of the rate of static yield stress evolution over time (RST) or 170 mm~200 mm of fluidity is established. This work provides theorical support for the control and evaluation of rheological properties in 3DPC.

Towards Ultrahigh Performance Concrete Produced with Aluminum Oxide Nanofibers and Reduced Quantities of Silica Fume.

Ultrahigh performance concrete (UHPC), which is characterized by dense microstructure and strain hardening behavior, provides exceptional durability and a new level of structural response to modern structures. However, the design of the UHPC matrix often requires the use of high quantities of supplementary cementitious materials, such as silica fume, which can significantly increase the cost and elevate the production expenses associated with silica fume handling. This paper demonstrates that a fiber-reinforced composite with properties similar to conventional UHPC can be realized with very low quantities of silica fume, such as 1% by mass of cementitious materials. The proposed UHPC is based on reference Type I cement or Type V Portland cement with very low C3A (<1%) that also complies with Class H oil well cement specification, silica fume, small quantities of Al2O3 nanofibers, and high-density polyethylene or polyvinyl alcohol macro fibers. Previous research has demonstrated that nanofibers act as a seeding agent to promote the formation of compact and nanoreinforced calcium silicate hydrate (C-S-H) clusters within the interparticle and nanofiber spaces, providing a nanoreinforcing effect. This approach produces a denser and stronger matrix. This research expands upon this principle by adding synthetic fibers to ultrahigh strength cement-based composites to form a material with properties approaching that of UHPC. It is indicated that the developed material provides improved strain hardening and compressive strength at the level of 160 MPa.

Use of borosilicate glass powder in cementitious materials: Pozzolanic reactivity and neutron shielding properties

This work evaluates both the pozzolanic reactivity and neutron shielding properties of cementitious paste and mortar mixtures containing varying amount of borosilicate glass powder. The experimental results indicate that the use of borosilicate glass powder results in a greater heat of hydration than that expected for cement paste alone at early ages (despite the fact that the cumulative heat release was reduced as the replacement of borosilicate glass powder increased). The maximum pozzolanic reactivity of borosilicate glass powder was estimated to be 55%, which was greater than a typical class F fly ash (≈30%). Borosilicate glass powder resulted in a 8% increase in the 28 d compressive strength of mortar for the replacement levels of up to 25% by mass. The neutron attenuation coefficient of mortar increased (10–40%) as the amount of borosilicate glass powder increased; however, it appears to plateau when the cement replacement ratio was higher than 25%. This plateau appears to be the result of competing effects (i.e., the addition of borosilicate glass powder continuously increases the attenuation coefficient while the reduction in hydration products reduces the attenuation coefficient). Based on initial testing, considering compressive strength and neutron shielding properties, the use of borosilicate glass powder in cementitious materials shows the best results when the replacement level is between 20 and 25% by mass of cementitious materials and when the cementitious system is properly cured. A simplified model was introduced to determine the required thickness of mortar with different mixture proportions for neutron shielding.

Effect of superabsorbent polymer characteristics on rheology of ultra-high performance concrete

Changes of rheological properties in ultra-high performance concrete (UHPC) suspending mortar incorporated superabsorbent polymer (SAP) were investigated. The effect of chemical composition of two SAP types (S1, acrylamide/acrylic sodium copolymer and S2, acrylamide polymer) and the S1 SAP with mean particle sizes of 95.1 and 471.3 μm on water absorption was evaluated. The effect of these parameter for dry SAP used at content of 0–0.6%, by mass of cementitious materials, on the rheology of the UHPC mortar was evaluated. The S1 SAP was also employed at 0.4% content in a pre-absorbed state to investigate the effect of the preconditioning method on the rheological properties. Test results show that the rheology of UHPC made with SAP depend on the water absorption/desorption properties. The water desorption after reaching the maximum water absorption limit for the S1 SAP can led to a decrease or stagnation of yield stress between 15 and 30 min of age. The increase in particle size of the SAP was shown to delay this stage of decrease or stagnation. The variation in yield stress of UHPC mortar made with the S2 SAP over time increased from 1 to 4 times compared to the reference mixture given the longer time for water absorption. The addition of the S1 SAP reduced the plastic viscosity and thixotropy, regardless of the size, content, and preconditioning method. The use of dry S2 SAP increased plastic viscosity by approximately 10 Pa.s and the thixotropy. The preconditioning method of SAP had no significant influence on thixotropy.

Iron slag as fine aggregate replacement and nanosilica particles in self-compacting concrete mixtures

A study of the mechanical behavior of self-compacting concrete mixtures under sand replacement (as fine aggregate) by iron slag (residue from industrial machining) from 0.0% to 50.0% of mass, variations of water/cementitious material ratio between 0.3 and 0.5 and nano SiO2 incorporation between 0.0% and 2.0% by mass of cementitious materials is presented. Fresh state tests of slump flow were performed, and the main rheological parameters: static yield stress and plastic viscosity were determined from a rheometer. For the hardened state, compressive strength tests were performed. The study of iron slag incorporation and water/cementitious materials ratio variation was developed based on a statistical methodology of central composite design from axial points based on a 2k factorial with central points, besides a posterior analysis of variance and Tukey’s multiple comparison tests. The optimization of these variables was developed using response surface methodology on 7 days compressive strength results, from the statistical design, besides the posterior determination of nano SiO2 effects on the optimized proportions. Among the most relevant results regarding the presence of iron slag, an increase in the early age compressive strength was found, with the optimized mixture strength being more than 100% higher than mixtures without iron slag at 7 days of curing. Regarding the effect of nano SiO2 addition to the optimized mixture, a detriment of the rheological parameters and a consequent reduction of the workability were the most remarkable findings. With the obtained results, iron slag proves to be a feasible sand replacement in self-compacting concrete mixtures.

Changes in rheology and mechanical properties of ultra-high performance concrete with silica fume content

High silica fume content used in ultra-high performance concrete (UHPC) can increase viscosity and render agglomeration issue, leading to reduction in mechanical properties, including bond to fibers. This study investigates the effect of silica fume content, ranging from 0 to 25%, by mass of cementitious materials, on rheological, fiber-matrix bond, and mechanical properties of non-fibrous UHPC matrix and UHPC made with 2% micro-steel fibers. Binary mixtures consisting of cement and silica fume with targeted mini-slump flow were specifically prepared. The involved mechanical properties include compressive, flexural, and tensile behavior. Rheology, fiber-matrix bond, flexural, and tensile strengths of UHPC were linked to each other using fiber dispersion and orientation analyses or the Composite Theory. Test results showed that UHPC made with 10% to 15% silica fume obtained the highest fiber-matrix bond, flexural, and tensile properties. Such silica fume content was found to result in lower viscosity and more uniformly distributed fibers as determined by image analysis. The flexural and tensile strengths of UHPC made with 5%–20% silica fume can be effectively predicted using the Composite Theory considering obtained fundamental inputs, such as flexural or tensile strengths of matrix, fiber characteristics, and fiber-matrix bond strength. The experimental-to-predicted tensile and flexural strength ratios were in the range from 0.9 to 1.1. However, the predicted strengths of UHPC mixtures with 0 and 25% silica fume were greatly lower than the experimental values due to high viscosity and low packing density.

Hydration, shrinkage, and durability of ternary binders containing Portland cement, limestone filler and metakaolin

A partial replacement of the clinker by latent hydraulic or pozzolanic materials is encouraged due to environmental and specific technical requirements. Such substitution remains limited to a relatively low level (less than 30% by mass of cementitious materials). An experimental research work was carried out on mortars made with binary and ternary binders (Portland cement; metakaolin; limestone filler) to reach 45% total replacement. In order to investigate the activating effect of reduced water-to-cement ratio, two series of mixtures were designed with W/C0 of 0.42 and 0.5. Their heat of hydration, portlandite content, shrinkage, porosity, and carbonation were monitored. The tests were performed to understand the evolution of their relative strength (activity index) and durability parameters. The strength development of mortars with ternary binders was found to depend on metakaolin properties, including manufacturing process and particle size distribution. Reducing W/C0 ratio accelerated pozzolanic reaction and allowed improving early-age strength and durability parameters.

Multi-scale investigation of microstructure, fiber pullout behavior, and mechanical properties of ultra-high performance concrete with nano-CaCO3 particles

The mechanical properties of a fiber-reinforced concrete are closely related to the properties of the matrix, fiber, and fiber-matrix interface. The fiber-matrix bond property is mainly governed by the adhesion between the fiber and surrounding cement materials, as well as the strength of materials at the interfacial transition zone. In this paper, the effect of nano-CaCO3 content, varying between 0 and 6.4%, by mass of cementitious materials, on microstructure development, fiber-matrix interfacial bond properties, and mechanical properties of ultra-high performance concrete (UHPC) reinforced with 2% steel fibers were investigated. The bond properties, including bond strength and pullout energy, were evaluated. Mercury intrusion porosimetry (MIP), backscattered electron microscopy (BSEM), optical microscopy, and micro-hardness testing were used to characterize the microstructure of matrix and/or interfacial transition zone (ITZ) around an embedded steel fiber. Test results indicated that the incorporation of 3.2% nano-CaCO3 significantly improved the fiber-matrix bond properties and the flexural properties of UHPC. This was attributed to densification and strength enhancement of ITZ as observed from micro-structural analyses. Beyond the nano-CaCO3 content of 3.2%, the fiber bond and mechanical properties of UHPC decreased due to increased porosity associated with agglomeration of the nano-CaCO3.

Effect of nano-SiO2 particles and curing time on development of fiber-matrix bond properties and microstructure of ultra-high strength concrete

Bond properties between fibers and cementitious matrix have significant effect on the mechanical behavior of composite materials. In this study, the development of steel fiber-matrix interfacial bond properties in ultra-high strength concrete (UHSC) proportioned with nano-SiO2 varying between 0 and 2%, by mass of cementitious materials, was investigated. A statistical model relating either bond strength or pullout energy to curing time and nano-SiO2 content was proposed by using the response surface methodology. Mercury intrusion porosimetry (MIP) and backscatter scanning electron microscopy (BSEM) were used to characterize the microstructure of the matrix and the fiber-matrix interface, respectively. Micro-hardness around the embedded fiber and hydration products of the matrix were evaluated as well. Test results indicated that the optimal nano-SiO2 dosage was 1% in terms of the bond properties and the microstructure. The proposed quadratic model efficiently predicted the bond strength and pullout energy with consideration of curing time and nano-SiO2 content. The improvement in bond properties associated with nano-silica was correlated with denser matrix and/or interface and stronger bond and greater strength of hydration products based on microstructural analysis.

Effects of Shrinkage Reducing Agent and Expansive Admixture on the Volume Deformation of Ultrahigh Performance Concrete

This paper investigated the influences of shrinkage reducing agent and expansive admixture on autogenous and drying shrinkage of ultrahigh performance concrete (UHPC) containing antifoaming admixture. The shrinkage reducing agent was used at dosage of 0.5%, 1%, and 2% and the expansive admixture was used at dosage of 2% to 4% by mass of cementitious material. The results show that the air content of UHPC increases with the higher addition of shrinkage reducing agent and expansive admixtures. However, the fluidity, compressive strength, and shrinkage of UHPC exhibit a declining tendency. The usage of expansive agent at dosage of 4% significantly reduces the shrinkage of UHPC. The 7-day autogenous shrinkage was decreased by 16.0% and 28-day drying shrinkage was decreased by 29.5%, respectively. Shrinkage reducing agent at dosage of 2% reduced the 7-day autogenous shrinkage by 44.3% and 28-day drying shrinkage by 50.2%. Compared with expansive admixture, shrinkage reducing agent exhibits more efficient shrinkage reduction effect on UHPC.

Effects of different nanomaterials on hardening and performance of ultra-high strength concrete (UHSC)

Nanomaterials have attracted much interest in cement-based materials during the past decade. In this study, the effects of different nano-CaCO3 and nano-SiO2 contents on flowability, heat of hydration, mechanical properties, phase change, and pore structure of ultra-high strength concrete (UHSC) were investigated. The dosages of nano-CaCO3 were 0, 1.6%, 3.2%, 4.8%, and 6.4%, by the mass of cementitious materials, while the dosages of nano-SiO2 were 0, 0.5%, 1.0%, 1.5%, and 2%. The results indicated that both nano-CaCO3 and nano-SiO2 decreased the flowability and increased the heat of hydration with the increase of their contents. The optimal dosages to enhance compressive and flexural strengths were 1.6%–4.8% for the nano-CaCO3 and 0.5%–1.5% for the nano-SiO2. Although compressive and flexural strengths were comparable for the two nanomaterials after 28 d, their strength development tendencies with age were different. UHSC mixtures with nano-SiO2 showed continuous and sharp increase in strength with age up to 7 d, while those with nano-CaCO3 showed almost constant strength between 3 and 7 d, but sharp increase thereafter. Thermal gravimetry (TG) analysis demonstrated that the calcium hydroxide (CH) content in UHSC samples decreased significantly with the increase of nano-SiO2 content, but remained almost constant for those with nano-CaCO3. Mercury intrusion porosimetry (MIP) results showed that both porosity and critical pore size decreased with the increase of hydration time as well as the increase of nanoparticles content to an optimal threshold, beyond which porosity decreased. The difference between them was that nano-CaCO3 mainly reacted with C3A to form carboaluminates, while nano-SiO2 reacted with Ca(OH)2 to form CSH. Both nano-CaCO3 and nano-SiO2 demonstrated nucleation and filling effects and resulted in less porous and more homogeneous structure.

Influence of Chloride-Ion Adsorption Agent on Chloride Ions in Concrete and Mortar

The influence of a chloride-ion adsorption agent (Cl agent in short), composed of zeolite, calcium aluminate hydrate and calcium nitrite, on the ingress of chloride ions into concrete and mortar has been experimentally studied. The permeability of concrete was measured, and the chloride ion content in mortar was tested. The experimental results reveal that the Cl agent could adsorb chloride ions effectively, which had penetrated into concrete and mortar. When the Cl agent was used at a dosage of 6% by mass of cementitious materials in mortar, the resistance to the penetration of chloride ions could be improved greatly, which was more pronounced when a combination of the Cl agent and fly ash or slag was employed. Such an effect is not the result of the low permeability of the mortar, but might be a result of the interaction between the Cl agent and the chloride ions penetrated into the mortar. There are two possible mechanisms for the interaction between the Cl agent and chloride ion ingress. One is the reaction between calcium aluminate hydrate in the Cl agent and chloride ions to form Friedel’s salt, and the other one is that calcium aluminate hydrate reacts with calcium nitrite to form AFm during the early-age hydration of mortar and later the NO2− in AFm is replaced by chloride ions, which then penetrate into the mortar, also forming Friedel’s salt. More research is needed to confirm the mechanisms.

Effect of Fly Ash and nanoCaCO&lt;sub&gt;3&lt;/sub&gt; on the Setting Time of Cement Paste

This paper presents an experimental study to evaluate the effects of fly ash and nanoCaCO3 on setting time of cement paste. The test group included the contents of fly ash was 30%, 40%, 50%, 60% and content of nanoCaCO3 was 2.5%, 5%, 10%, 20%. Results indicate that setting time was increased with the incorporation of fly ash, shortened with the incorporation of nanoCaCO3. The incorporation of 5% nanoCaCO3 by mass of cementitious materials reduced initial and final setting times by 60 and 70 min, respectively. In comparison to the referenced paste with 40% fly ash. The best fly ash content appear to be 40% when nanoCaCO3 was added.

Use of nano-silica to increase early strength and reduce setting time of concretes with high volumes of slag

Abstract The effects of nano-silica (NS) on setting time and early strengths of high volume slag mortar and concrete have been experimentally studied. Effects of NS dosages, size and dispersion methods on strength development of high volume slag mortars were also investigated. A constant water-to-cementitious materials ratio (w/cm) 0.45 was used for all mixtures. The results indicate that the incorporation of a small amount of NS reduced setting times, and increased 3- and 7-day compressive strengths of high-volume slag concrete, significantly, in comparison to the reference slag concrete with no silica inclusion. Compressive strength of the slag mortars were increased with the increase in NS dosages from 0.5% to 2.0% by mass of cementitious materials at various ages up to 91 days. The strengths of the slag mortars were generally increased with the decrease in the particles size of silica inclusions at early age. Ultra-sonication of nano-silica with water is probably a better method for proper dispersion of nano-silica than mechanical mixing method.

Drying Shrinkage Behavior of Mortars Made with Ternary Blends

Ternary cementitious blends are widely used in today's concrete mixtures, particularly when high performance is needed. This paper discusses drying shrinkage behavior of mortar mixtures made with various ternary blends. Ternary blends consisting of different combinations of portland or blended cement, slag, fly ash, and silica fume were considered. The amounts of slag, fly ash, and silica fume ranged from 15% to 35%, 13% to 30%, and 3% to 10% by mass of cementitious materials, respectively. Mortar bars were made with the ternary blends and subjected to drying (i.e., temperature = 73° ± 3°F and relative humidity = 50% ± 4%) after standard moist curing for 28 days. Free shrinkage of the bars was assessed at 56 days of age after 28 days of drying. A response surface analysis was done to examine the effects of blend proportions on shrinkage behavior of the mortars. To validate this model, an independent group of mortar mixtures with different ternary combinations was cast, and the measured values were compared with the predicted shrinkage values. The results indicated that of the three supplementary cementitious materials in the ternary blends studied, slag showed a dominant effect on increasing mortar shrinkage. The contribution of Class C fly ash to the shrinkage was slightly less than that of slag. An increase in silica fume or in Class F fly ash content slightly increased free shrinkage. There is a good correlation between the measured shrinkage strain and the strain predicted from the shrinkage model developed from the response surface analysis.

Crack Resistance of Concrete with Incorporation of Light-Burnt MgO

The advanced Temperature and Stress Test Machine was introduced to evaluate the cracking resistance of concrete with inclusion of light-burnt MgO under full restraint by tracking thermal and deformation development. Results showed that light-burnt MgO being incorporated ranging between 4 per cent and 6 per cent by mass of cementitious materials was beneficial to increase the maximum compressive stress and cracking stress of concrete by 0.37MPa and 0.2MPa on average respectively. The maximum temperature was slightly reduced from 59.8°C to 66.2°C while cracking temperature was significantly decreased from 0.8°C to minus 5.6°C. Sensitive anti-cracking coefficient F was forwarded to assess the early cracking tendency of concrete and in general, inclusion of 4 per cent light-burnt MgO with activity of 109s was rated the best in crack resistance.

Performance of Polypropylene Fiber and Rubber Powder Improved High Strength Concrete

Based on high strength concrete (HSC), the improved HSC concrete was produced by adding different contents of fine grain rubber particles and polypropylene fibers. The grain size of the rubber particle is 420 m and the rubber content is 1%, 2%, and 3% of the mass of cementitious material respectively. The volume fraction of polypropylene fiber is 0.1%.The performance of HSC, rubber particle improved high strength concrete (RHSC), polypropylene fiber improved high strength concrete (PHSC) and polypropylene fiber hybrid rubber particle improved high strength concrete (PRHSC) before and after high temperature are studied. The investigation methods used are the external surface inspection, weight loss and residual strength testing. The experimental results show that rubber particles can improve the workability of HSC and PHSC under normal temperature. Polypropylene fiber can significantly improve the spalling failure resistance property of HSC and RHSC.