Portland Cement Fly Ash Research Articles

Chloride diffusivity in flexural cracked Portland cement concrete and fly ash concrete beams

In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete (PCC) and fly ash concrete (FAC), were tested with various crack widths. Total 14 reinforced concrete (RC) beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing (RCT) method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors kf and kw can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.

Heat of hydration of Portland high-calcium fly ash cement incorporating limestone powder: Effect of limestone particle size

This study investigated the limestone powder (LS) particle size effect on the heat of hydration of Portland cement (PC) and high-calcium fly ash (FA) systems. The LS used has a maximum particle size of 5 and 20μm, respectively. Isothermal calorimetry was used to measure the heat evolution during the hydration process of the cement and PC–FA pastes. The results show the particle size of LS had a significant influence on the observed heat of hydration both on rate of reaction and total amount of heat release. The hydration rates of both PC–LS and PC–FA–LS systems were accelerated by 5μm LS, while 20μm LS did not. For PC–FA–LS system, the total heat release at 48h when using 5μm LS were higher than FA at 30% replacement level whereas 20μm LS showed similar total heat release. However, the total heat release of these ternary mixtures with both LS particle sizes was still lower than PC control. X-ray diffraction (XRD) technique and thermogravimetric (TG) analysis were applied to identify the hydration products. XRD results show the formation of carboaluminates and ettringite was still found at 28days, indicated the stabilization of ettringite when both LS particle size were used. The reaction between LS and PC or FA was confirmed by TG results in the reduction of CaCO3 content.

Decalcification of activated paper sludge – Fly ash-Portland cement blended pastes in pure water

Decalcification in pure water of ternary Portland cement (TPC) pastes, containing thermally activated paper sludge and fly ash, has been evaluated from the leaching of Ca2+ in pure water at the temperature of 20°C during 90days. Monitoring of calcium loss showed that the leaching kinetics are controlled by diffusion. The degradation of the material over time is estimated from the calcium effective diffusivity. A similar study of plain ordinary Portland cement (OPC) pastes was carried out for comparison. The results showed lower effective diffusion coefficients of calcium in the case of the TPC pastes. This behaviour is related to its microstructure, which is denser than that of OPC as a result of the pozzolanic activity of both additions.

Mechanical Properties of Cement Mortar Containing Fine-Grained Fraction of Fly Ashes

This paper presents the effect of fly ash grain-size fractions on Portland-fly ash cement hydration and its properties. Siliceous fly ashes of size fraction of 0 - 16 and 16 - 32 μm, separated from initial fly ash samples from 1st, 2nd and 3rd hopper in ESP system, were analysed. Cement hydration was investigated by determination of hydration heat and content of Ca(OH)2 and C3S in cement samples. Water to cement ratio and initial setting time of cement pastes as well as compressive strength and microstructure of cement mortars were also analyzed. Results showed that the same amount of the same size ash fraction can give cement of lower or higher early strength and its lower or higher increase with time. Incorporation of 20 wt% of ash fraction of 0 - 16 μm can produce Portland-fly ash cement CEM II/A-V of strength class 42.5R (from 2nd hopper) or 52.5N (from 3rd hopper). Cement containing 40 wt% of ash fraction of 0 - 16 μm from 2nd and 3rd hopper can be classified as pozzolanic cements CEM IV/A-V of strength class 42.5 and normal or rapid early strength, respectively. Different development of strength of cement with addition of the same size ash fraction separated from the initial ash sample from the next hopper in ESP system is connected with higher depolymerization degree of SiO4 units in ash glass, resulting from the greater amount of AlO4 units replacing SiO4 units. Ash fraction of 16 - 32 μm shows lower depolymerisation of glass network and as a consequence lower hydration degree of C3S to portlandite and calcium silicate hydrates (C-S-H).

Research on Performance Concrete Made with Slay-Fly Ash and Ground Limestone

Base on experimental studying, early strength and work performance of portland cement, slay cement and fly ash cement improves and enhances when added ground limestone into and the adding content is beyond 8% .The strength of concrete is better than ordinary concrete, early strength increases by 16.9% when added ground limestone into and the adding content is beyond 10%. By studying on experiment, the strength of concrete which has been added slay and fly ash into when added ground limestone into and the adding content is 10% improves more than strength of concrete that has only adds slay or fly ash into. The fluidity of concrete that has added slay and fly ash into when added ground limestone into and the adding content is 10% lose small, this character is good at concrete construction. This experiment provides help for us to select concrete additive admixture and make good use of industrial waste.

Durability of stabilised galvanic sewage sludge against the impact of sea water and sulfate solutions

Solidification of industrial sludge in concrete matrices has been examined. The concrete mixes in which galvanic sewage sludge was immobilised were prepared with the use of two binder types: Portland-fly ash cement CEM II/B-V, and a binder composed of Portland cement (60%) and fly ash obtained from fluidized bed combustion of fuels (40%). Leaching of heavy metals (Cr, Cd, Zn, Ni, Cu, Pb, V) was observed from solidification matrices which had been exposed to various aqueous media (distilled water, sea water, sulfate solution) over a long period of time. Features of concrete were also studied which could directly influence the release of heavy metals, i.e. their microstructures and microporosity. Moreover, the effect of sewage sludge addition was shown on physical and mechanical properties of concrete, i.e. compression strength, water absorbability and water penetration depth were analysed. The research programme covered the periods of 1 year and 2 years, during which the concrete samples were stored in various aqueous environments. The stability parameters of the matrix which contained fly-ash from fluidized bed combustion of fuels were found not to be much different from the parameters for the matrix which was based on the Portland-fly ash cement. Leachability of heavy metals was demonstrated to increase in the aggressive aqueous medium as compared to the level obtained when the samples were stored in distilled water.

Effect of Active Magnesia on the Properties of Cementitious Binders

ABSTRACTReactive magnesium oxide (magnesia, MgO) was produced by calcining magnesite at comparatively low temperature, less than 800 ℃C. The reactive MgO and fly ash were used as additives to cementitious binder. The reactive MgO-ordinary Portland cement-fly ash is referred to as MgO-OPC-FA cement in further. The hydration expansion effect of active magnesia on the properties of cementitious binder in different mixing ratio was investigated. It is known that the “dead burnt” MgO reacts with water very slowly, which causes the expansion after the solidification of cement. Therefore, the MgO content in ordinary cement is commonly restricted to less than 5%. Effects of reactive MgO on the expansion properties of the cementitious binders were studied. Hydrated products of reactive MgO cements were investigated by X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis. The MgO-OPC-FA cement was sound, although the content of reactive MgO in cement was about 8 wt. %. Reactive MgO was hydrated at early age in 24 hours, thus causing rapid expansion. Mg(OH)2appeared on initial stage of cement hydration for active magnesia. The hydration rate of active magnesia was not equal to that of the dead burnt magnesia. The hydration of reactive MgO has a negative effect on the mechanical properties of reactive MgO-ordinary Portland cement-fly ash system, in spite of the inhibitive effect of the expansion of MgO hydration produced by fly ash. Our results shed light on the potential utilization of reactive MgO in the manufacturing of cementitious binders.

Durability of fly ash/GGBFS based geopolymers exposed to carboncapture solvents

This paper examines a series of fly ash and ground granulated blast furnaceslag binders formulated to examine the effects of composition and mix designon performance and durability when exposed to aggressive environments foundin carbon capture facilities (monoethanolamine or concentrated potassiumcarbonate, as well as distilled water). Ordinary Portland cement andordinary Portland cement fly ash blends were examined for comparison. Thesamples are exposed to solvents by immersion under static conditions. Leachingand mechanical strength tests show a wide range of geopolymer performance,depending on the initial mix design and the nature of the aggressive agent.Alkali carbonate solutions are found to be the most aggressive agent amongthose tested in terms of geopolymer mass and strength loss; nonetheless, theresistance to structural degradation upon carbonation of the geopolymer binderstructure is mitigated to a significant extent by the low calcium contentof the geopolymer binder. Less porous materials, or materials with smallerand more tortuous pores, show in many cases a markedly higher durability;porosity is shown to hold the key to durability. In traditional cement basedbinders, strength is lost through chemical attack upon exposure to solvents.

Multicompound Model for the Hydration of Portland Cement–Fly Ash Binders

In this study, traditional reaction equations (based on the theory of Powers) are applied to the hydration reactions of portland cement and the pozzolanic reaction of fly ash separately. Moreover, portland clinker is considered as a mixture of four minerals, each with its own sensitivity to the presence of fly ash. The kinetics of the reactions of each clinker mineral have been analyzed by fitting generally known models such as the Avrami and Jander equations to isothermal heat measurements on pastes of cement, fly ash, and water. The proposed model therefore consists of different stages, in which nucleation, phase-boundary, and diffusion reactions become rate controlling. The kinetics of the pozzolanic reactions have been described with similar equations, implementing parameter values based on measured selective dissolution data. Fly ash may accelerate the reaction of a clinker mineral, while at the same time it can decelerate another mineral. Depending on the relative proportions of the clinker minerals, the method can explain the apparent contradiction found in literature related to the acceleration or deceleration effect of fly ash on the cement hydration.

Utilization of fly ash with silica fume and properties of Portland cement–fly ash–silica fume concrete

This paper reports the normal consistency, setting time, workability and compressive strength results of Portland cement–fly ash–silica fume systems. The results show that water requirement for normal consistency was found to increase with increasing SF content while a decrease in initial setting time was found. Workability, measured in term of slump, was found to decrease with silica fume content (compared to blends without silica fume). However, it must be noted that despite the reduction in the slump values, the workability of Portland cement–fly ash–silica fume concrete in most cases remained higher than that of the Portland cement control concrete. Furthermore, the utilization of silica fume with fly ash was found to increase the compressive strength of concrete at early ages (pre 28 days) up to 145% with the highest strength obtained when silica fume was used at 10 wt%. Moreover, scanning electron micrographs show that utilization of fly ash with silica fume resulted in a much denser microstructure, thereby leading to an increase in compressive strength.

Microstructural, physical, and thermal analyses of Portland cement–fly ash–calcium hydroxide blended pastes

The effect of calcium hydroxide (CH) on the properties of Portland–fly ash cement pastes, at up to high-volume fly ash mixes has been investigated using normal consistency, setting time, compressive strength, thermal analysis and scanning electron microscope. CH as an additive material (5 and 10 wt%), lignite fly ash (FA) up to 50 wt% was used to produce Portland cement (PC)–FA–CH pastes at w/PC + FA ratio of 0.5. Water requirement for normal consistency was found to increase with increasing CH content while a decrease in initial setting time was found. Furthermore, the compressive strengths of all FA mixes with CH were found to be higher than the mixes without CH. Thermal analysis and scanning electron microscope were used to study the hydration of PC–FA–CH system. The results showed that the first phase transition detected by thermal analyses was attributed to ettringite, calcium silicate hydrate, gehlenite hydrate and was found to be higher in PC–FA–CH mixes than in pure Portland–FA cement paste resulting in an increase in compressive strength. Moreover, the hydration phases were also found to increase with increasing curing time. Overall, the results show that the additional of 5 wt% CH in Portland–FA mixes especially at high-volume FA mixes was found to accelerate FA pozzolanic reaction at early ages (7 and 28 days), resulting to an increase in compressive strength.

Thermal analysis and microstructure of Portland cement-fly ash-silica fume pastes

Thermal analysis (thermogravimetry and differential thermal analysis) was used with scanning electron microscopy technique to investigate the hydration mechanisms and the microstructure of Portland cement-Fly ash-silica fume mixes. Calcium silicate hydrate (C–S–H), ettringite, gehlenite hydrate (C2ASH8), calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3) phases were detected in all mixes. In the mixes with the use of silica fume addition, there is a decrease in Ca(OH)2 with increasing silica fume content at 5 and 10% compared to that of the reference Portland-fly ash cement paste and a corresponding increase in calcium silicate hydrate (C–S–H).

Influence of Aggregate Type and Size on Ductility and Mechanical Properties of Engineered Cementitious Composites

The influence of aggregate type and size on engineered cementitious composite (ECC) mechanical and ductility properties was investigated and the results presented in this paper. A micromechanically-based high-performance fiber-reinforced cementitious composite, ECC enjoys improved durability and high ductility due to tight crack width. Microsilica sand (200 μm [0.008 in.] maximum aggregate size) is typically used to produce standard ECC mixtures. There was investigation of ECC mixtures containing either gravel sand or crushed dolomitic limestone sand with maximum sizes of 2.38 or 1.19 mm (0.094 or 0.047 in.) in this study. Three different ECC mixtures with 1.2, 2.2, and 4.2 fly ash/portland cement (FA/C) ratios were cast for each aggregate type and maximum aggregate size. There was experimental determination of crack development, drying shrinkage behavior, and the effects of FA/C, aggregate type, and maximum aggregate size on compressive, flexure, and unixial tensile properties. Experimental results show that strain-hardening behavior with strain capacities, provided that the matrix employs a high FA content, can be compared with the standard microsilica sand ECC mixtures, in ECC mixtures produced with gravel sand and crushed dolomitic limestone sand with higher maximum aggregate sizes. Tensile strengths of these mixtures can be 3.57 to 5.13 MPAa (0.52 to 0.74 ksi), and tensile ductility can maintain, at 28 days of age, 1.96 to 3.23%. Material behavior can be further improved by using crushed dolomitic limestone sand and gravel sand, since they can be drying-shrinkage arrestors in the paste.

Mathematical model of strength and porosity of ternary blend Portland rice husk ash and fly ash cement mortar

This paper presents a mathematical model for strength and porosity of mortars made with ternary blends of ordinary Portland cement (OPC), ground rice husk ash (RHA) and classified fly ash (FA). The mortar mixtures were made with Portland cement Type I containing 0-40% FA and RHA. FA and RHA with 1-3% by weight retained on a sieve No. 325 were used. Compressive strength and porosity of the blended cement mortar at the age of 7, 28 and 90 days were determined. The use of ternary blended cements of RHA and FA produced mixes with good strength and low porosity of mortar. A mathematical analysis and two-parameter polynomial model were presented for the strength and porosity estimation with FA and RHA contents as parameters. The computer graphics of strength and porosity of the ternary blend were also constructed to aid the understanding and the proportioning of the blended system.

EFFECTS OF TIME INTERVAL FOR PLACING ON CONSOLIDATED FRESH CONCRETE AND THE BONDING STRENGTH WITH VARIOUS CEMENTS

Recently, increasing various constructions, we can choose various cement for each concrete constructions, suited their performance. We studied properties and time interval for placing on consolidated fresh concrete with fresh concrete with ordinary portland cement, moderate-heat portland cement, portland blast-furnace slag cement, portland fly ash-cement, and eco-cement. And we prepared influence of the durability of placing joint. The results suggested, ordinary portland cement had high compressive strength and eco-cement had less bleeding water. Additionally, the results showed the time interval of placing influenced the termination time of bleeding with various cements.

The calcium silicate hydrates

This article is concerned with the calcium silicate hydrates, including crystalline minerals and the extremely variable and poorly ordered phase (C-S-H) that is the main binding phase in most concrete. Up-to-date composition and crystal-structure information is tabulated for the most important crystalline calcium (alumino) silicate hydrates and related phases. A number of models for the nanostructure of C-S-H are summarized and compared and it is shown that there is much more of a consensus than might seem apparent at first sight. The value of the recently solved structures of 1.4 nm tobermorite and jennite, together with those of jaffeite and metajennite, for visualizing the nanostructural elements present in the models is demonstrated. The importance of Hal Taylor's contribution to the solution of the structure of jennite is highlighted. The applicability of Richardson and Groves' model is demonstrated using experimental composition-structure observations on the nature of C-S-H in a Portland cement-fly ash blend.

Morphology and nanostructure C–S–H in white Portland cement–fly ash hydrated at 85°C

The C–S–H present in water and alkali activated hardened pastes of neat white Portland cement (WPC) and blends of WPC with 30% fly ash hydrated at 85°C has been characterised. The chemical composition of C–S–H could not be determined by SEM–EDX because of intermixing with other phases; TEM–EDX was necessary. The mean Ca/(Al–Si) atomic ratio of C–S–H was lower in the water activated blend than in the neat cement paste due to the reaction of the fly ash. The fibrillar morphology of outer product C–S–H in the water activated neat cement paste was coarser than that formed at lower temperatures. The mean length of the aluminosilicate anions in the C–S–H was much higher than in C–S–H formed at lower temperatures and was higher in the blended pastes than with neat cement. The composition–structure data are discussed in terms of models for the nanostructure of C–S–H. The lattice parameter a inferred from compositional data for the hydrogarnet phase in the water activated blend was in good agreement with the value measured directly by XRD.

Studies on cement and mortar containing low-calcium fly ash, limestone, and dolomitic limestone

The effects of low-calcium fly ash (FA), limestone (LS), and dolomitic limestone (DLS) on the properties of cement and mortar has been investigated through a number of tests. Composition of cement hydration products in cement paste and mortar were made with clinker (PC), gypsum (G), FA, LS and DLS. The binders employed were Portland cement (OPC), fly ash–portland cement (FA–OPC), FA–LS–OPC, and FA–DLS–OPC blends with a maximum PC replacement level of 40%, FA level of up to 40%, LS and DLS levels of up to 15%. The hydration rate and products were studied by means of X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FTIR). The results showed that the FA, LS and DLS prolong the setting time of the cements. Relative to OPC, in FA–OPC system expansion decreases as the fly ash content of the cement increases. Ternary system, FA–DLS–OPC produces a marked fall in the expansion of the tested specimens.

Development of volcanic pumice based cement and lightweight concrete

The results of investigations on the suitability of using volcanic pumice (VP) as cement replacement material and as coarse aggregate in lightweight concrete production are reported. Tests were conducted on cement by replacing 0–50% of cement by mass and on concrete by replacing 0–100% of coarse aggregate by volume. The physical and chemical properties of VP were critically reviewed to evaluate the possible influence on both fresh and hardened properties of cement and concrete. The standard tests on different mixtures of Portland cement and volcanic pumice powder (VPP) mixtures provided encouraging results, comparable to those for blended Portland fly ash cement, and showed good potential for manufacturing Portland volcanic pumice cement with higher setting time and low heat of hydration using up to 15% of VPP. The properties of volcanic pumice concrete (VPC) using different percentages of volcanic pumice aggregate were evaluated by conducting a comprehensive series of tests on workability, strength, shrinkage and permeability. It is concluded that VPC has sufficient strength and adequate density to be accepted as structural lightweight concrete. Design charts are presented to evaluate mix design parameters of VPC.

Using neural networks to predict workability of concrete incorporating metakaolin and fly ash

This paper details the development of neural network models that provide effective predictive capability in respect of the workability of concrete incorporating metakaolin (MK) and fly ash (FA). The predictions produced reflect the effect of graduated variations in pozzolanic replacement in Portland cement (PC) of up to 15% MK and 40% FA. The results show that the models are reliable and accurate and illustrate how neural networks can be used to beneficially predict the workability parameters of slump, compacting factor and Vebe time across a wide range of PC–FA–MK compositions.