Blended Cement Pastes Research Articles

Enhancing the hardened properties of blended cement paste cured at 0 °C by using alkali-treated ground granulated blast furnace slag

The use of high-volume ground granulated blast furnace slag (GGBFS) in cement-based materials significantly reduces CO2 emissions. Nevertheless, low curing temperatures are barriers to using environmentally friendly materials in winter construction works. This is mainly attributed to slow GGBFS's reactivity and blends' strength development due to the low alkalinity offered by the slow hydration rate of Portland cement (PC) at low temperatures. In this study, sodium hydroxide was employed to produce dry reactive pre-alkali-activated GGBFS (A-GGBFS), with an intention to increase the system's alkalinity and reactivity. The blended cement paste was prepared with 50% PC replacement with untreated and treated GGBFS, and cured constantly at 0 °C for 28 days. The A-GGBFS accelerated the hydration rate and enhanced the precipitation of hydration products. By adding an optimal NaOH content during the pre-alkali-activation process, the 3 and 28 days compressive strengths of paste increased by 41% and 37%, respectively, gaining a comparable 28 days compressive strength to that measured in a 100% PC-based binder. The microstructural assessments are consistent with compressive strength measurements.

Recycling of Flash-Calcined Dredged Sediment for Concrete 3D Printing

Due to the large volumes of sediments dredged each year and their classification as waste materials, proper management is needed to efficiently dispose of or recycle them. This study aimed to recycle flash-calcined dredged sediment in the development of an eco-friendly 3D-printable mortar. Mortars with 0, 5, 10, 15, 20, and 30% of flash-calcined sediment were studied. Two tests were carried out to determine the printability of the mixtures. First, a manual gun device was used to examine the extrudability, then a modified minislump test was conducted to assess the buildability and shape-retention ability of the mixtures. Furthermore, the flow table test and the fall cone test were used to evaluate the workability and structural buildup, respectively. The compressive strength was also evaluated at 1, 7, and 28 days for printed and nonprinted mortar specimens. In addition, isothermal calorimetry measurements were conducted on corresponding cement pastes. The results showed that it was possible to print mortars with up to 10% of flash-calcined sediment with the preservation of extrudability and buildability. The results showed that flash-calcined sediment shortened the setting time, decreased the flowability, and enhanced the shape-retention ability. Nonprinted samples with 5% and 10% of flash-calcined sediment showed a similar to higher compressive strength compared to that of the reference mortar. However, printed samples recorded an equal to lower compressive strength than that of nonprinted samples. In addition, no significant change in the hydration process was detected for blended cement pastes compared to the reference cement paste.

Degradation mechanism of blended cement pastes in sulfate-bearing environments under applied electric fields: Sulfate attack vs. decalcification

Applied electric fields, the reason behind stray currents, accelerate the ingress of sulfate into cementitious materials. To identify mitigation approaches, this study investigates the effects of slag and fly ash on sodium sulfate attacks of cement pastes under a constant electric current. The mineralogical alterations induced by the attacks were analyzed using X-ray diffractometry, thermogravimetric analysis, scanning electron microscopy, and thermodynamic modeling. The dissolution of aluminates in the slag and fly ash induced a monosulfate-rich area (>∼20 mm from the cathode surface) to form next to the ettringite-rich area on the sample surface (<∼20 mm). This effect reduced the availability of SO42− in the pore solution, thereby hindering the penetration of sulfate. Meanwhile, the consumption of portlandite by the pozzolanic reaction lowered the decalcification resistance of the materials. This produced a wide area that endured the decomposition of portlandite and carbonate-AFm. Overall, blending 30% fly ash did not improve the resistance of the material to either sulfate attacks or decalcification; blending 50% slag can effectively mitigate sulfate ingress, though decalcification may become a governing mechanism in the degradation process.

The effect of paste composition, aggregate mineralogy and temperature on the pore solution composition and the extent of ASR expansion

The reaction kinetics of the alkali silica reaction depends on the composition of the pore solution. The evolution of the pore solution composition in different cement pastes and concretes was studied. Pastes containing silica fume or metakaolin had the lowest amount of alkalis in the pore solution. In addition, metakaolin increased the aluminium concentrations. The lowest expansion was measured for the concretes made of blended cement pastes with low alkali and hydroxide content in their pore solution, for the duration of the present study, no additional aluminium effect was observed due to the already low pH. Addition of 400 mM of Li slowed down expansion rate of concrete prisms at 40 and 60 °C, however, similar expansion was observed for samples with and without Li at 60 °C after 1 year. Temperature, alkali concentration and pH of pore solution all have a major effect on ASR expansion.

Valorization of deep soil mixing residue in cement-based materials

This study examined the potential of recycling deep soil mixing residue (DSMR), a cement-soil waste, as a partial Portland cement substitute. The chemical and mineral compositions of DSMR before and after calcination were determined. For the calcined DSMR blended cement pastes, the compressive strength and phase assemblage (characterized using TGA and XRD) were evaluated. Results revealed pozzolanic and hydraulic properties of the calcined DSMR, due to the formation of reactive calcium-rich glassy phases and hydraulic C2S. The calcined DSMR can contribute to the strength development of cement because of the pozzolanic reactions and the formation of additional hydrates. With up to 20% calcined DSMR, negligible side-effect on the strength of the blended cement paste was noticed. The compressive strength development of the blended cement pastes was linearly correlated to the reactive phase content in the calcined DSMR. This work demonstrated the potential of using DSMR to develop greener composite cement.

Impact of C-S-H seeding on hydration and strength of slag blended cement

The impact of C-S-H seeding on the hydration of slag blended cement was systematically investigated, trying to understand and explore the potential of C-S-H seeding in blended cement. Three levels of substitution of cement by slag were investigated: 50, 75 and 95 wt%. Compressive strength, calorimetry, in-situ and fresh disc XRD experiments were carried out. Results show that C-S-H seeding improves the performance of slag blended cement significantly with regards to strength at early and later stage. Quantitative XRD analyses show how C-S-H seeding influences the clinker hydration kinetics. The microstructure of hardened blended cement paste was investigated using electron microscopy and mercury intrusion porosimetry. The results show that C-S-H seeding altered the microstructure dramatically by refining the porosity. Correlation of strength to heat release and pore structure indicates that there is structural impact of C-S-H seeding besides the impact on kinetics in the hardened samples.

Influence of Copper and Zinc Tailing Powder on the Hydration of Composite Cementitious Materials.

Copper and zinc tailing powder (CZTP) is finely ground waste after copper minerals and zinc minerals have been extracted from ores during beneficiation. CZTP has certain potential cementitious properties and can be used in composite cementitious materials. The pore size distribution and hydrate phase assemblage of the hardened samples are investigated using MIP and XRD. SEM is employed to examine the microstructure of the specimens. The chemically bonded water is used to measure the degree of hydration. CZTP lowers the hydration heat evolution rate and the total hydration heat. The hydration heat evolution rate reduces as the w/b ratio rises, whereas the total hydration heat of blended cement paste rises. CZTP diminishes the strength development of the Portland-CZTP system, and the strength decreases as the CZTP level increases. CZTP reduces the critical pore diameters of the Portland-CZTP system with w/b = 0.3 after curing for 3 d and 28 d, while increasing the critical pore diameters of samples with w/b = 0.45 at the same age. CZTP increases the gel micropores of Portland-CZTP. Although CZTP increases the pore volume content of blended cement pastes with w/b = 0.3, the volume of harmful pores decreases. The pore volume content of the Portland-CZTP system decreases as the w/b ratio increases. However, the volume of harmful pores increases with a higher w/b ratio. The main hydration products in the Portland-CZTP system are portlandite, ettringite, and C-S-H. CZTP mainly played the role of filling or acting as a microaggregate in the Portland-CZTP system.

Particle-size effect of recycled clay brick powder on the pore structure of blended cement paste

Herein, based on the selected particle sizes of 0–25 μm, 25–45 μm and 45–75 μm, the particle-size effect of recycled clay brick powder (RCBP) on the pore structure of blended cement pastes was investigated. Results show that RCBP particle size has a significant impact on the pore size and pore volume distributions and pore surface fractal dimension of blended paste throughout the observed age and on porosity and tortuosity only at later ages. Reducing RCBP particle size proved effective in improving the pore structure of blended paste. Notably, tortuosity is strongly correlated with compressive strength in an exponential correlation.

Mechanical properties and durability of ternary blended cement paste containing rice husk ash and nano silica

Many researchers are using Rice husk ash (RHA) as pozzolanic admixture. Pozzolanic admixture is an amorphous aluminosilicate materials, which may not be naturally cementitious, but react with calcium hydroxide (Ca(OH)2) and water to form cementitious compounds. Further, many researchers also found that the use of Nano silica (NS) in Portland cement (PC) enhances the mechanical properties as well as durability. The present study reports on the addition of RHA and NS into PC, aiming to assess the influence of the RHA and NS on the strength and durability properties of mixture. The pastes were prepared to perform compressive strength test, Flexural strength test, Ultra Pulse Velocity (UPV) test, Water absorption test, Acid attack test and XRD analysis. Compressive strength results showed a substantial improvement in samples containing NS. The highest compressive strength and flexural strength are found in the PC-based mixture containing RHA (10%) and NS (3%) after 28 days of hydration. PC-based mixture containing RHA (10%) and NS (3%) shows reduction of water absorption and mass loss under acid attack at 28 days. It is also seen that a combination of 10% RHA and 3% NS in paste led to a positive contribution to durability properties. Synergistic effect can be seen in mixtures incorporating RHA (10%) and NS (3%). Therefore, it supports the use in fabrication of cementitious materials.

Investigation of sulfate attack on aluminum phases in cement-metakaolin paste

Al-containing phases such as stratlingite, C-A-S-H, and TAH play an essential role in studying the sulfate attack of MK blended cement paste. This paper investigates the sulfate attack of various aluminate hydrate products commonly formed in metakaolin (MK) blended cement paste and the evolution of aluminate hydrate products of the cement-MK paste under sulfate attack. The results show that both the synthesized stratlingite and the stratlingite produced by the cement-MK paste have excellent sulfate attack resistance. Additions of 30% and 50% MK consume all portlandite produced by the cement hydration and result in the formations of C-A-S-H, stratlingite, TAH, and C4AH13. For the 30% MK blended cement paste under sulfate attack, C4AH13 reacts with SO42− to form ettringite at the beginning because of its poor sulfate resistance. Once C4AH13 is consumed, SO42− directly targets the stratlingite, C-A-S-H, and TAH due to no portlandite in the system; C-A-S-H and TAH are the two primary contributors of Ca2+ ions and Al3+ ions to the ettringite formation. The ettringite formation is suppressed due to the absence of CH, and the existence of stratlingite, C-A-S-H, and TAH reduces the content of reactive Al that can react with sulfate.

Cement-Biofouling and Sulfate Resistivity of Hardened Blended Cement Pastes in Marin Environment: A Case Study

In the present study, field examinations are explored on diversed blended cement mixes. The hardened blended pastes are prepared using ordinary Portland cement (OPC), fine metakaolin (MK) and brine chlorine sludge(CLS). Cement fouling features and the attack by SO4-2 ions are studied on the blended samples that are immersed in the sea water for 9 months. The performance of the cured specimens was explored via studying the compressive strength, the percent of mass change and the volume expansion at various curing durations. Besides, the total chlorophyll colonized on the surface of the cured specimens was determined by using spectrophotometeric technique. XRD and SEM techniques are specifed for studying the phase compositions and the morphology of the formed cement hydrates. The results illustrate that the blended mixes show an antifouling behavior higher than the neat OPC. This is related to acquiring a more compact structure of reduced porosities upon OPC blending. Additionally, OPC-MK specimens showed higher SO-42 ions resistance than OPC-CLS or OPC pastes. This is related to the high pozzolanic properties of MK in contrary to brine sludge.

A compressive strength prediction model based on the hydration reaction of cement paste by rice husk ash

The effect of partial replacement of cement by unground residual rice husk ash (RHA) on the workability and compressive strength of concrete was investigated in this work. In addition, the hydration products were also investigated in the blended cement paste by X-ray diffraction. An optimal replacement ratio model and a compressive strength prediction model were established based on the effect of RHA on the hydration reaction of cement paste. Evaluation of models was carried out using different statistical indicators. The results showed that the addition of RHA in concrete had a negative effect on the workability of fresh concrete, and the mechanical properties of concrete are optimal when the content of RHA is 20%. It has been verified that the established prediction model corrects well with the experimental results.

Hydration and Mechanical Properties of Blended Cement with Copper Slag Pretreated by Thermochemical Modification.

The application of granulated copper slag (GCS) to partially replace cement is limited due to its low pozzolanic activity. In this paper, reconstituted granulated copper slag (RGCS) was obtained by adding alumina oxide (Al2O3) to liquid copper slag. Blended cement pastes were formulated by a partial substitute for ordinary Portland cement (OPC) with the RGCS (30 wt%). The pozzolanic activity, mechanical development, and the microstructure were characterized. The results show that 5–10 wt% Al2O3 contributes to the increase in magnetite precipitation in RGCS. The addition of Al2O3 alleviates the inhibition of C3S by RGCS and accelerates the dissociation of RGCS active molecules, thus increasing the exothermic rate and cumulative heat release of the blended cement pastes, which are the highest in the CSA10 paste with the highest Al2O3 content (10 wt%) in RGCS. The unconfined compressive strength (UCS) values of blended cement mortar with 10 wt% Al2O3 added to RGCS reach 27.3, 47.4, and 51.3 MPa after curing for 7, 28 and 90 d, respectively, which are the highest than other blended cement mortars, and even exceed that of OPC mortar at 90 d of curing. The pozzolanic activity of RGCS is enhanced with the increase in Al2O3 addition, as evidenced by more portlandite being consumed in the CSA10 paste, forming more C-S-H (II) gel with a higher Ca/Si ratio, and a more compact microstructure with fewer pores than other pastes. This work provided a novel, feasible, and clean way to enhance the pozzolanic activity of GCS when it was used as a supplementary cementitious material.

Enhancing the effectiveness of steam curing for cement paste incorporating fly ash based on long-term compressive strength and reaction degree of fly ash

Steam-cured concrete plays an imperative role in contemporary construction, particularly in the urban region where the progress of the project is one of the main keys for cost savings. However, steam curing can cause several adverse impacts on the mechanical and durability performances of concrete in long term. The macroscale properties of concrete are mainly controlled by the properties of cement paste. This research aims to find out the appropriate treatment stage of steam curing on blended cement paste and the optimum quantity of fly ash substituted in the paste that not only can achieve the design strength in short term but also be able to alleviate the detrimental impacts of heat treatment in long term. Cement pastes incorporating 0, 20, 35, and 50 wt% fly ash were mixed at a water/binder ratio of 0.28 and cast into the mold with a size of 50 × 50 × 50 mm. Then, these paste specimens were treated with the treatment stage at 55 °C, 70 °C, and 85 °C for various hours. The compressive strength and the hydration degree of fly ash were measured over 545 days. The results indicated that the treatment stage with the temperature of 70 °C applied for 4 h existed to be adequate to promote the early strength while the substitution of 35% fly ash happened to be the optimum quantity.

Hydration Behaviour and Characteristics of Binary Blended Metakaolin Cement Pastes

Cement production consume large amount of energy to form clinker and carbon dioxide (CO2) emitted into the atmosphere causing global warming. To mitigate this challenge, the use of Metakaolin (MK) as supplementary cementitious material cannot be over emphasized. This study evaluated the use of Metakaolin (MK) on hydration development of MK--PC blended cements and strength of Mortars. The MK with a Blaine fineness of 7883 cm2/g was used to replace Portland Cement (PC) at a level of 0, 5, 10, 15, 20, 25 and 30 % by mass of PC at a constant w/b ratio of 0.50 to prepare blended cements. Hydration development of blended cement and compressive strength of Mortars were investigated using chemically bond water and free-lime contents and strength tests respectively. X – Ray diffraction (XRD) and scanning electron Microscopy (SEM) techniques were also utilised in the analysis of Pozzolanic reaction and hydration products. Test results indicates that Water of consistency, setting times for the mixes increased with increase in MK contents, influence of MK on the chemically bond water and free Lime contents of the blended cements were due to its filler and dilution effects and Pozzolanic reaction. The cumulative non-evaporable water and free-lime contents increased by partial replacement of PC with MK due to PC hydration and Pozzolanic reaction. The tested Mortar prepared with blended cements with 30 % PC replacement with MK shows a retardation of strength development with a low value at early ages (7 days) and increased in growth at later ages (28 days). The compressive strength of tested mortar for 90 days curing age for the blended mortar is 31 N/mm2 close to that of control Mortar (35 N/mm2). The results obtained from XRD and SEM analysis indicated increase in Calcium Hydroxide (CH) consumption and Calcium Silicate hydrate (C-S-H) formation in blended cement pastes with curing time. The PC replacement with MK induced changes in Microstructures of blended cement paste and chemical composition of hydration products. These results are potentials for modelling the behaviour of MK-PC blended cements.

Evaluation of the phase composition, microstructure, mechanical performance, and resistance to acid attack of blended cement paste composed of binary trass-cement system

This study comprehensively investigated the viability of binary blended trass-cement system for being used as a competitive alternative to cement or other traditional blended cements. Concerning the phase composition, the trass blended sample had not only higher gel contents, but also faster rates of gel formation, which were 1.5 and 1.2 times greater than those of the plain cement sample during the periods of 7–28 and 28–90 days, respectively. Regardless of the samples types, the increase rate of ultrasonic pulse velocity was highest within the interval of 3–7 days, then decreased during the period of 7–28 days, and almost approached zero at 28–90 days. This indicated the minor change of the samples microstructure at prolonged ages compared to those earlier ones. Due to the pozzolanic effect of trass, the pore size distribution significantly shifted toward smaller pore diameters and also became more uniform. Furthermore, the filler effect of trass reduced the total intruded volume and total porosity by 11.7% and 9.2%, respectively. In the case of mechanical performance, the blended sample showed higher compressive strengths, whereas slightly lower flexural ones in comparison to its plain counterpart, which could be owing to the changes in phase composition and microstructure induced by blending cement with trass. Lastly, it was revealed that the nitric acid attack, by progressively decalcifying the exposed samples, gradually transformed them into soft, cracked, and highly porous materials with new microstructural morphology and mineralogical composition. This way, substantial losses in their performance and integrity happened over immersion time.

Hydration development of blended cement paste with granulated copper slag modified with CaO and Al2O3

Granulated copper slag (GCS) is currently applied to partial cement replacement as a supplementary cementitious material (SCM), but with a low rate due to its low pozzlanic activity. In this contribution we introduce an approach to enhance the reactivity of GCS by modifying the mineral structure using calcium oxide (CaO) and aluminum oxide (Al2O3) both by 10 wt.%, in a molten state. Blended cement pastes were formulated using cement (70 wt.%) and the modified GCS (30 wt.%). The development of hydration heat and strength were examined using isothermal calorimetry and strength tests, respectively. The mineral composition and microstructure of hydration products for different reaction periods were examined using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Also, toxicity characteristic leaching procedure (TCLP) was performed on the samples. Results showed an increase in the hydration heat emission rate from the early hydration and the compressive strength of blended cement paste after curing for 28 days, indicating that the addition of CaO and Al2O3 in GCS improves pozzolanic activity. XRD and SEM-EDS analysis indicated that the modified GCS consumed more calcium hydroxide (CH) accompanied by increased generation of calcium silicate hydrate (C–S–H) gels in blended cement with a microstructure containing more gel phases and fewer pores, forming a more compact structure. Leaching of heavy metals of paste samples was lower than Environmental Protection Agency (EPA) limit. It is possible to apply the modified GCS as a sustainable material to promote cleaner production for cement and concrete industries.

Insights on chemical and physical chloride binding in blended cement pastes

This study investigates chloride binding in blended cement pastes exposed to 0.5 M NaCl solutions (with and without pH adjustment) using X-ray diffraction and energy-dispersive X-ray spectroscopy image analysis (edxia). The aim is to better understand the effects of the binder type, the water-to-binder ratio and the pH on the chemical binding in AFm phases and the physical binding on C-A-S-H. Results show that the binding cannot be predicted from AFm and C-A-S-H contents alone because competing ions in the system affect both the Friedel's salt solid solution chemistry and the C-A-S-H binding capacity. Notably, the high content of aluminous hydrates in LC3 systems leads to a high chemical binding even if Friedel's salt solid solutions have relatively low chloride contents (particularly at a higher pH). On the contrary, the CEMIII/A paste showed low binding because of relatively high sulfate and magnesium contents which compete for incorporation/adsorption in aluminous hydrates (AFm, ettringite and hydrotalcite).

Upcycling coal- and soft-series metakaolin in blended cement with limestone

In a ternary blended cement system, metakaolin together with limestone are often applied as replacement of cement to mitigate the carbon emissions of concrete production. This research examined and compared the performance when replacing cement with coal or soft-series metakaolin (CMK and SMK) and limestone at different levels of substitution (15–60%). The synergistic effect between hydration reaction, pozzolanic reaction, and limestone reaction were studied to understand the mechanism. At a lower cement substitution level (15–30%), the pozzolanic reactivity dominated the strength development, hence SMK samples are found to have higher compressive properties than that of corresponding CMK samples. However, with further increasing of cement substitution (>45%), the synergy effect of CMK with limestone can compensate for the strength loss due to the formation of a higher amount of reactant carboaluminate for pore refinement. The overall performance shows that it is feasible to upcycle CMK with limestone at high substitution levels (45–60%) for the production of sustainable blended cement paste.

Acetic Acid Modified Steel Slag via Dry Chemical Modification Method for Enhancing the Hydraulic Reactivity

To activate the early-age hydraulic reactivity of steel slag powder (SS), a method of using acetic acid (AA)-anhydrous alcohol solution to modify the SS via dry chemical modification technology was proposed. The compressive strength and hydraulic reactivity of SS pastes and SS blended cement pastes were investigated, then the mineral composition, surface morphology and specific surface area of unmodified SS and AA modified SS were characterized. The results show that calcite, portlandite and dicalcium ferrite in SS react with AA to produce calcium acetate and pores in the modified process, thus leading to AA modified SS with the greater specific surface area and rougher surface. Water is easier to absorb onto the surface of modified SS and enters the inner of SS particles along the pores, resulting in higher dissolution heat and reaction heat of active minerals in SS. The result show that, the higher 72 h cumulative hydration heat, the 3 d, 7 d and 90 d compressive strengths of AA modified SS pastes and AA modified SS blended cement pastes are obtained, compared to the unmodified pastes.