Replacement Of OPC Research Articles

Physico-chemical characteristics of blended cement pastes containing electric arc furnace slag with and without silica fume

Filled-pozzolanic cement pastes were made by different replacements of OPC by electric arc furnace slag (EAFS) with silica fume (SF) at water/cement ratio of 0.27. The pastes were hydrated up to 90days. At each time interval, the physico-chemical characteristics of the hardened cement pastes were studied and related to the structure of the hardened pastes and the role of EAFS replacement as a filler in the hardened OPC-EAFS pastes. It was found that the optimum replacement of OPC by EAFS for the improvement in hydraulic properties of filled cement pastes is 6%. High replacement of OPC by EAFS (10% or 15%) causes a notable deterioration in the compressive strength at all ages of hydration. The replacement of EAFS in Mix (90% OPC+10% EAFS) by 4% SF causes a marked improvement in the mechanical properties for the hardened pastes of Mix (90% OPC+6% EAFS+4% SF). The DSC thermograms for all pastes indicated the formation of nearly amorphous calcium silicate hydrates, calcium sulphoaluminate hydrates, calcium aluminate hydrates and portlandite. The SEM micrographs showed that the partial substitution of OPC by EAFS and/or SF leads to more dense structures as compared to the neat OPC paste.

The Influence of Burning Temperature of MIRHA On Mechanical Properties of Foamed Concrete

Microwave incinerator as one of the modern incinerators is proposed to produce amorphous Microwave incinerated Rice Husk Ash (MIRHA) with high pozzolanic reactivity thus can significantly enhance concrete properties. Analyses on the MIRHA with various burning temperature, the temperatures used were 300°C, 400°C, 500°C, 600°C and 800°C. To determine the physical and chemical properties of MIRHA with various burning temperature were also conducted through X-ray diffraction (XRD), X-ray Fluorescence (XRF), scanning electron microscope (SEM) and mechanical properties test. The results showed that the MIRHA at 300 o C could be used as a cementitious material with optimum OPC replacement at 20%. It was found that MIRHA foamed concrete at 300 o C achieved more than 100% higher strength compared to foamed concrete without MIRHA.

The fracture response of blended formulations containing limestone powder: Evaluations using two-parameter fracture model and digital image correlation

The fracture response of mortars in which OPC is partially replaced by limestone or a combination of limestone and fly ash/metakaolin (i.e., for total OPC replacement levels of 20% and 35% by volume) is reported. The blended mortars demonstrate fracture parameters (fracture toughness, KICS and critical crack tip opening displacement, CTODc, determined using the two-parameter fracture model, TPFM) that are comparable to or better than those of pure OPC formulations in spite of having slightly lower compressive strengths than the OPC systems. The ternary blends containing limestone and metakaolin at 20% OPC replacement show the best performance: a consequence of the beneficial limestone–alumina synergy that has been previously established. The strain energy release rates also show trends that are in line with the other fracture parameters. The fracture parameters for selected mixtures evaluated through a non-contact digital image correlation technique are found to correspond well to those determined from TPFM. The outcomes highlight that improved ductility can be attained through the judicious use of limestone and synergistic OPC replacement materials.

Utilization of high volumes of unprocessed lignite-coal fly ash and rice husk ash in self-consolidating concrete

Abstract This paper describes a study undertaken to explore the use of a high volume of lignite coal fly ash (FA) as a replacement for Type I Portland cement (OPC) and a high volume of rice husk ash (RHA) as a replacement for fine aggregate in the production of self-consolidating concrete (SCC). OPC was partially replaced with 0%, 20%, 40%, and 60% FA by volume, and fine aggregate was replaced with 0%, 25%, 50%, 75%, and 100% RHA by volume. Mixtures were designed based on a slump flow diameter of 70 ± 2.5 cm. The workability properties ( i.e. slump flow, T 50 cm slump flow time, V-funnel flow time, and J-ring flow) and hardened properties ( i.e. compressive strength and ultrasonic pulse velocity) of SCC were determined, and a blocking assessment was performed. Increasing the FA or RHA content beyond a certain level reduced the compressive strength and increased the water requirement of the SCC mixture. However, up to 60% FA could be used to produce SCC with a compressive strength of 40–50 MPa. In addition, RHA could comprise up to 25% of the SCC, which is an acceptable value of compressive strength according to the Building Code Requirements. Moreover, partial replacement of OPC by FA and fine aggregate by RHA can result in substantial cost savings and alleviate environmental problems.

Pozzolanic and hydraulic activity of nano-metakaolin

Nano-metakaolin (NMK) was prepared by firing of Nano-kaolin (NK) at different temperatures (750–825°C) for 2h. The pozzolanic activities of NMK samples were studied using hydrated lime as an activator. The optimum firing temperature of metakaolin (MK) was established from the results of hydration kinetics and differential scanning calorimetry (DSC) and found to be 750°C; NMK, thus produced, is designated as NMK(750). This was based on the marked consumption of free calcium hydroxide by NMK fired at 750°C as well as the highest values of chemically combined water at all ages of hydration. Therefore, NMK(750) was used for partial replacement of OPC and studying the physico–mechanical properties of OPC–NMK blended cement pastes. The optimum substitution of OPC by NMK was found to be 8–10%. This was based on the development of compressive strength of the various hardened OPC–NMK blended cement pastes having different NMK contents (0–16%), where the strength increases with NMK content up to 10% and then decreases. In addition, the SEM micrographs obtained for the hardened OPC (93%)–NMK (7%) blended cement paste displayed the formation of amorphous and microcrystalline CSH which fill the pores leading to a more dense structure with higher hydraulic activity as compared to neat OPC paste.

Feasibility tests on concrete with very-high-volume supplementary cementitious materials.

The objective of this study is to examine the compressive strength and durability of very high-volume SCM concrete. The prepared 36 concrete specimens were classified into two groups according to their designed 28-day compressive strength. For the high-volume SCM, the FA level was fixed at a weight ratio of 0.4 and the GGBS level varied between the weight ratio of 0.3 and 0.5, which resulted in 70–90% replacement of OPC. To enhance the compressive strength of very high-volume SCM concrete at an early age, the unit water content was controlled to be less than 150 kg/m3, and a specially modified polycarboxylate-based water-reducing agent was added. Test results showed that as SCM ratio (R SCM) increased, the strength gain ratio at an early age relative to the 28-day strength tended to decrease, whereas that at a long-term age increased up to R SCM of 0.8, beyond which it decreased. In addition, the beneficial effect of SCMs on the freezing-and-thawing and chloride resistances of the concrete decreased at R SCM of 0.9. Hence, it is recommended that R SCM needs to be restricted to less than 0.8–0.85 in order to obtain a consistent positive influence on the compressive strength and durability of SCM concrete.

Effect of Relative Levels of Mineral Admixtures on Strength of Concrete with Ternary Cement Blend

In the present scenario to fulfill the demands of sustainable construction, concrete made with multi-blended cement system of OPC and different mineral admixtures, is the judicious choice for the construction industry. Silica fume (SF) and fly ash (FA) are the most commonly used mineral admixtures in ternary blend cement systems. Synergy between the contributions of both on the mechanical properties of the concrete is an important factor. This study reports the effect of replacement of OPC by fly ash (20, 30, 40 and 50 % replacement of OPC) and/or silica fume (7 and 10 %) on the mechanical properties of concrete like compressive strength and split tensile strength, with three different w/b ratio of 0.3, 0.4 and 0.45. The results indicate that, as the total replacement level of OPC in concrete using ternary blend of OPC + FA + SF increases, the strength with respect to control mix increases up to certain replacement level and thereafter decreases. If the cement content of control mixes at each w/b ratio is kept constant, then as w/b ratio decreases, higher percentage of OPC can be replaced with FA + SF to get 28 days strength comparable to the control mix. A new method was proposed to find the efficiency factor of SF and FA individually in ternary blend cement system, based on principle of modified Bolomey’s equation for predicting compressive strength of concrete using binary blend cement system. Efficiency factor for SF and FA were always higher in ternary blend cement system than their respective binary blend cement system. Split tensile strength of concrete using binary and ternary cement system were higher than OPC for a given compressive strength level.

Role of Filler Effect and Pozzolanic Reaction of Biomass Ashes on Hydrated Phase and Pore Size Distribution of Blended Cement Paste

The role of filler effect and pozzolanic reaction of biomass ash on hydrated phase and pore size distribution of blended cement paste was studied. Rice husk ash (RHA), palm oil fuel ash (POFA), and river sand (RS) were ground to two fineness values, and used to replace Type I portland cement (OPC) at 0, 20, and 40% by weight of binder. A water to binder ratio of 0.35 was used. The compressive strength, pore size distribution, and thermogravimetric analyses of the blended cement pastes were investigated. Partial replacement of OPC with fine RHA and POFA at a dosage of 20% by weight of binder resulted in pastes with higher compressive strengths than that of OPC paste. The compressive strengths of RHA paste were slightly higher than those of POFA pastes at the same age. The differences between mass losses (at 30–450°C) of RS and RHA (or POFA) blended pastes at the same fineness, curing time, and replacement rate were due to the pozzolanic reaction, which increased in accordance with particle fineness and cement replacement rate. In addition, the weight losses (at 30–450°C) due to the pozzolanic reaction were higher than those due to the filler effect. The use of fine RHA and POFA enhanced the pozzolanic reaction, and reduced the average pore diameters of pastes.

Compressive Strength of Cement Mortar Using Sebha Clay, Treated by Sonication Method

Clay as natural pozzolan is found in the north of the city of Sebha, Libya. Sebha clay is relatively high in silica, and its physical and chemical properties could be referred to as ASTM C618 class N. Sonication treatment is carried out and the treated Sebha clay is used as a mineral admixture in the Portland cement mortar. Horn method 20 kHz frequencies with different powers and different times are used in the Sonication treated. The particle size distributions (PSD) and Scanning Electron Microscope (SEM) imaging are used to understand the mechanism of pozzolanic improvement of the Sebha clay after treatment by sonication. This paper shows the physical and chemical properties of sonication treat Sebha clay. The effect of magnitude of sonic power on pozzolanic activity of treated kaolin is investigated. The main aim of the present research is to study the strength characteristics of cement mortar using Sebha natural clay after sonication is treated as a partial replacement of ordinary Portland cement OPC. The parameters are investigated, including compressive strengths .The results show enhancement in particle size and pozzolanic activity of treated kaolin, with increase in sonic power and in the time.

Cellular lightweight concrete containing high-calcium fly ash and natural zeolite

Cellular lightweight concrete (CLC) with the controlled density of approximately 800 kg/m3 was made from a preformed foam, Type-I Portland cement (OPC), fly ash (FA), or natural zeolite (NZ), and its compressive strength, setting time, water absorption, and microstructure of were tested. High-calcium FA and NZ with the median particle sizes of 14.52 and 7.72 μm, respectively, were used to partially replace OPC at 0, 10wt%, 20wt%, and 30wt% of the binder (OPC and pozzolan admixture). A water-to-binder mass ratio (W/B) of 0.5 was used for all mixes. The testing results indicated that CLC containing 10wt% NZ had the highest compressive strength. The replacement of OPC with NZ decreased the total porosity and air void size but increased the capillary porosity of the CLC. The incorporation of a suitable amount of NZ decreased the setting time, total porosity, and pore size of the paste compared with the findings with the same amount of FA. The total porosity and cumulative pore volume decreased, whereas the gel and capillary pores increased as a result of adding both pozzolans at all replacement levels. The water absorption increased as the capillary porosity increased; this effect depended on the volume of air entrained and the type or amount of pozzolan.

Hydration and strength development in ternary portland cement blends containing limestone and fly ash or metakaolin

This paper reports the influence of limestone particle size and the type of (partial) cement replacement material on hydration and the mechanical properties of cement pastes. Limestone powders having median particle sizes of 0.7, 3, and 15μm, at OPC replacement levels between 0% and 20% (volume basis), and two other replacement materials of differing reactivity (i.e., Class F fly ash or metakaolin) at replacement levels between 0% and 10% (volume basis), are used to proportion ternary binder formulations. Fine limestone accelerates early-age hydration, resulting in comparable or better 1-day compressive strengths, and increased calcium hydroxide (CH) contents as compared to pure cement pastes. The incorporation of metakaolin in conjunction with limestone powder alters the heat release (i.e., kinetic) response significantly. A ternary blend of this nature, with 20% total cement replacement demonstrates the highest 1-day strength and lowest CH content. Thermal analysis reveals distinct peaks corresponding to the formation of the carboaluminate phases after 28days in the limestone–metakaolin modified pastes, whereas the incorporation of similar levels of fly ash does not change the response markedly. It is shown that the synergistic effects of limestone and metakaolin incorporation results in improved properties at early ages, while maintaining later age properties similar to that of traditional OPC systems.

Retardation effect and corrosion detection of blended cement pastes

Different blended cement pastes were prepared from OPC+10%, 20% and 30% slag (air cooled) by using a water/solid ratio (W/S) of 0.25 (by weight). The hydration was conducted for various time intervals at 1, 3, 7, 28 and 90days. Each hardened cement paste was tested for its physico-chemical and mechanical characteristics under normal curing conditions. In addition, the phase compositions of the formed hydration products were identified by means of X-ray diffraction (XRD). Moreover, the electrical conductivity and corrosion detection measurements were also carried out for all the previous blended cements under investigation. The results showed that the combined water contents increase gradually with hydration time for all hardened cement pastes and the partial replacement of OPC by slag cause a notable drop in the combined water content for all blend pastes. The compressive strength values obtained for the hardened blended cement pastes is less than that of neat OPC pastes at all ages of hydration up to 90days but the sample with 30% slag+70% OPC had the highest compressive strength. The electrical conductivity of the studied blended cement pasts was lower than that of OPC due to less alkali hydroxides when cement is diluted by the added slag. The significance of low potentials of steel bars in these pastes indicates inhibition of corrosion. As a result, it can be concluded that the mineral admixtures retards the hydration and inhibit the corrosion for cement pastes.

Performance of Concrete at Elevated Temperatures: Utilizing A Blended Ordinary Portland Cement (Opc)/ Saw Dust Ash (Sda) As Binder

This study aimed at investigating the effect of subjecting concrete, produced with cement being partially replaced with saw dust ash (SDA) to elevated temperatures. The performance of the test concrete cubes was done by exposing them to elevated temperatures of 200oC, 400oC, 600oC and 800oC, and allowed to cool down to room temperature before testing for their properties. Both the physical and thermal properties of the concrete cubes were determined. The concrete produced by blending cement with 10% SDA with an average percentage loss of 23.04% retained more of its compressive strength when exposed to the different temperatures, than concrete produced using only OPC, which has an average percentage loss of 29.11%. It is also found that, at an elevated temperature of 800oC, concrete fail totally in flexure due to the effect of high heat on binding elements. The flexural strength of both the control concrete (at 0% OPC replacement) and OPC/SDA blended concrete (at 10% OPC replacement) decreased as the temperature is increased. The replacement of OPC by 10% SDA increased the thermal shock resistance of the concrete by 11 cycles than the 0% OPC concrete at the same temperature. The concrete produced with OPC has better thermal conductivity than the concrete produced by blending OPC with SDA, as a result, the dislodgement of the concrete edges is relatively lower in the SDA blended cement concrete than in the OPC concrete. The result shows that, blending OPC with SDA in concrete performed better at elevated temperatures than concrete produced with only OPC. Therefore, the replacement of OPC with 10% SDA can be applied as a fire resisting bonding material in concrete.

Hydration of multicomponent composite cement: OPC-FA-SF-MK

Hydrations of OPC, OPC-FA, OPC-FA-SF and OPC-FA-SF-MK were studied by measuring water consistency, setting times, free lime, water percolation, air permeability, compressive strength and expansion in corrosive atmosphere. FTIR and DTA studies were also made on the hydrated samples. Results have shown that even 40wt.% replacement of OPC by FA+SF+MK does not deteriorate the quality of cement. The compressive strength is higher than any of the combination even at 3days of hydration. The pozzolanic materials act as a filler as well as increase the formation of C–S–H phase, the main glue.

Use of ground palm oil fuel ash to improve strength, sulfate resistance, and water permeability of concrete containing high amount of recycled concrete aggregates

This study proposes the use of ground palm oil fuel ash (POFA) with high fineness to improve the mechanical properties and durability of concrete containing high amount of recycled concrete aggregates. The mixture proportions of the recycled aggregate concretes were separated into two groups; the first group was composed of 100% coarse recycled aggregate and natural river sand, while the second group was composed of 100% both coarse and fine recycled aggregates. A portion of ordinary Portland cement type I (OPC) was replaced by ground POFA at 20%, 35%, and 50% by weight of binder for both recycled aggregate concrete groups. The results showed that ground POFA could improve the compressive strength and reduce the water permeability of recycled aggregate concretes. With 20% replacement of OPC by ground POFA, the compressive strength of recycled aggregate concretes was only 7% lower than that of the conventional concrete. The modulus of elasticity of recycled aggregate concrete with and without ground POFA was lower than that of the conventional concrete by approximately 25%. Finally, ground POFA could be used effectively to reduce the expansion of recycled aggregate concrete. As the replacement of ground POFA in concrete is increased, the expansion of recycled aggregate concrete due to sodium sulfate attack decreased.

Carbonation durability of blended cement pastes used for waste encapsulation

Blended cement pastes are currently used for encapsulation of low level and intermediate level nuclear waste in the UK. However, there is still little information on the long-term durability of those mixes to some chemical attacks. Accelerated testing may predict the long-term durability or at least help the selection of more durable formulations. In this work, blended blastfurnace slag (BFS)/Portland cement (OPC) pastes containing 60, 75 and 90% BFS and pulverised fuel ash (PFA)/OPC pastes with 40, 55 and 75% PFA were cured at 20 and 60°C for 90 days then submitted to natural and accelerated carbonation (5% CO2). The effects of the curing temperature as well as the OPC replacement level on the carbonation ratio are presented. Results showed a good correlation between natural and accelerated carbonation for the pastes studied. Carbonation was found to be governed by the amount of calcium hydroxide available in the mixes before the process started.

Chloride Ions Penetration Resistance of Steam-Cured Concrete for Railway Precast Elements

By use of ASTM C1202, this paper studied the influence of mineral admixtures on the chloride ions penetration resistance of the steam-cured concrete. The experimental results indicated that mineral admixtures improved the permeability properties of high-performance concretes, but at different rates depending on the binder type. FA required a relatively longer time to get its beneficial effect. For each 10%~40% replacement of OPC by FA in a concrete mix, the values of coulomb charge of steam-cured and standard curing concrete reduces by 8%~17% at180 days. When 30% weight of the OPC were replaced by FA and ground blast furnace slag(GBFS), the inclusion of 30% mineral admixtures provided a significant improvement to the chloride ions penetration resistance properties of steam-cured and standard curing concrete at 28 days and 180 days, especially for the combination of 10% FA and 20% GBFS (double adding).

Developmental stage of oligodendrocytes determines their response to activated microglia in vitro

BackgroundOligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes are both lost in central nervous system injury and disease. Activated microglia may play a role in OPC and oligodendrocyte loss or replacement, but it is not clear how the responses of OPCs and oligodendrocytes to activated microglia differ.MethodsOPCs and microglia were isolated from rat cortex. OPCs were induced to differentiate into oligodendrocytes with thyroid hormone in defined medium. For selected experiments, microglia were added to OPC or oligodendrocyte cultures. Lipopolysaccharide was used to activate microglia and microglial activation was confirmed by TNFα ELISA. Cell survival was assessed with immunocytochemistry and cell counts. OPC proliferation and oligodendrocyte apoptosis were also assessed.ResultsOPCs and oligodendrocytes displayed phenotypes representative of immature and mature oligodendrocytes, respectively. Activated microglia reduced OPC survival, but increased survival and reduced apoptosis of mature oligodendrocytes. Activated microglia also underwent cell death themselves.ConclusionActivated microglia may have divergent effects on OPCs and mature oligodendrocytes, reducing OPC survival and increasing mature oligodendrocyte survival. This may be of importance because activated microglia are present in several disease states where both OPCs and mature oligodendrocytes are also reacting to injury. Activated microglia may simultaneously have deleterious and helpful effects on different cells after central nervous system injury.

혼화재 종류 및 치환율이 콘크리트의 내염성능 향상에 미치는 영향에 관한 연구

This paper investigates the effect of the concrete containing mineral admixtures(pozzolanic materials such as fly-ash, ground granulated blast-furnace slag, silica fume and meta kaolin) on the resistance properties to chloride ion invasion. The purposed testing procedure was applied to the concrete replaced mineral admixtures for 34 replacement ratios under water-binder ratios ranged from 0.40 to 0.55. For the electro-migration test, Tang and Nilsson's method was used to estimate the diffusion coefficient of chloride ion. As a results, the water-binder ratios, kinds of mineral admixtures and replacement ratios, water curing periods had a great effect on the diffusion coefficient of chloride ion, and the optimal replacement ratios had a limitation for each mineral admixtures. Also, the use of mineral admixtures by mass(replacement of OPC) enhance the resistance ability against chloride penetration compared with the plain concrete. The compressive strength was shown related to the diffusion coefficient of chloride ion, the compressive strength increases with the diffusion coefficient of chloride ion decreasing. Below the 50 MPa, the variation of diffusion coefficient of concrete replaced mineral admixtures was bigger than that of plain concrete.

Color Laser Printer Using Four All-in-One Cartridges

A small color laser printer using four all-in-one cartridges has been developed. Four fan-shaped cartridges, each of which contains an OPC drum, a developing unit, a charger and a cleaner, are assembled into a rotary carousel. The carousel rotationally changes each color cartridge to produce primary color images that are superimposed onto an intermediate transfer belt to make a full-color image that is transferred to a paper all at once. This world-first color all-in-one cartridge eliminates hand-dirtying problems during toner and OPC replacement. Furthermore, fewer supply items and a 10,000-page long cartridge ensure less user intervention for the replacing of consumables. Its all-front-access structure, which is similar to conventional monochrome lasers, affords good user friendliness. This technology is employed in Panasonic's color laser printer DP-CL16.