Use of Plant-Based Accelerator to Enhance Rate of Gain of Strength of Kenyan Blended Cement

Concrete is the most widely used construction material in the world. The situation in the country is not an exception as most of the infrastructures in Kenya such as buildings, bridges, concrete drainage among others, are constructed using concrete. Sadly, the failure of buildings and other concrete structures is very common in Kenya. Blended Portland cement type 32.5 N/mm2 is the most widely used concrete binder material and is found in all parts of the country. Despite blended cement CEM 32.5 being the most commonly used cement type in construction industry in Kenya and most developing countries as a result of its low price and availability locally, its strength gain has been proven to be lower compared to when other types of cement are used due to quantity of pozzolanic material added to the blend. This paper outlines findings of an experimental investigation on the use of cypress tree extract as an accelerator to enhance rate of gain of strength on Kenyan blended cements. Six different blended cement brands locally available were used during the study. Cement chemical analysis was done using X-ray diffraction method while for the cypress extract, Atomic Absorption Spectrometer machine was used. Physical and mechanical properties were checked based on the British standards. The generation of the concrete mix design was done using the British DOE method and concrete was tested for the compressive strength at 7, 14, 21, 28, 56 and 90 days. It was observed that 15% dosage of the extract expressed as a mass percentage of the cement content gives the most improved compressive strength of concrete, 10.4% at 7 days and 9.5% at 28 days hence the optimum. It was further noted that when Cypress tree extract is used as an accelerator in the mix, the blended cement concrete achieves the design strength at 27 days saving 10 days of the project duration compared to when no accelerator is used while the ultimate strength is achieved at 67 days. The study therefore recommends the use of the cypress tree bark extract at a dosage of 15%, by mass, of the cement content as an accelerator when the structure is to be loaded at 28 days and waiting up to 39 days before loading the structure if no accelerator is used for blended cement concrete.

Effect of Coal Gangue with Different Kaolin Contents on Compressive Strength and Pore Size of Blended Cement Paste

The effects of activated coal gangue on compressive strength, porosity and pore size distribution of hardened cement pastes were investigated. Activated coal gangue with two different kaolin contents, one higher and one lower, were used to partially replace Portland cement at 0%, 10%, and 30% by weight. The water to binder ratio（w/b） of 0.5 was used for all the blended cement paste mixes. Experimental results indicate that the blended cement of activated coal gangue mortar with higher kaolin mineral content has a higher compressive strength than that with lower kaolin mineral content. The porosity and pore size of blended cement mortar were significantly affected by the replacement of activated coal gangue.

A Blended Cement Containing Blast Furnace Slag and Phosphorous Slag

Blended cement containing blast furnace slag (BFS) and phosphorous slag( PS) is a new kind of cement. The total content of blended materials could increase if two additives were used. Using the same admixtures , the properties of the blended cement with 70% additives could reach the standard of 525-grade slag cement according to GB. The strength of cement with 80% additives could reach the standard of 425-grade slag cement. The tests of strength, pore structure, hydration products, inhibiting alkali-aggregate reaction, resistance to sulfate corrosion of BFS-PSC were performed.

The Hydration of Blended Cement at Low W/B Ratio

The hydration process,hydration product and hydration heat of blended cement paste mixed with mineral admixture and expansive agent at low W/B ratio are studied by XRD,thermo analysis,and calorimetry instrument,and they were compared with those of pure cement paste.The results show that pure cement and blended cement at low W/B ratio have the same types of hydration products,but their respective amounts of hydration products of various blended cements at same ages and the variation law of the amount of same hydration products with ages are different;The joint effect of tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore and rift caused by the crystalloid ettringite is the impetus of the volume expansion of cement paste,and the former effect is much greater than the latter one.

Hydrothermal Characteristics of Blended Cement Pastes Containing Silica Sand Using Cement Kiln Dust as an Activator

The hydrothermal reactivity of silica sand was studied using cement kiln dust (CKD) as an activator in addition to the Portland cement fraction of El-Karnak cement (a blend of ordinary Portland cement and ground sand). Autoclaved EI-Karnak cement pastes were studied at pressures of 0.507, 1.013 and 1.520 MPa of saturated steam with respect to their compressive strength, kinetics of hydrothermal reaction and the phase composition of the formed hydrates. The role of CKD in affecting the physicochemical and mechanical properties of EI-Karnak cement pastes was studied by autoclaving of several pastes containing 5, 7.5, 10 and 20% CKD at a pressure of 1.013 MPa of saturated steam. CKD was added either as a raw CKD (unwashed) or after washing with water (washed CKD). The results of these physicochemical studies obtained could be related as much as possible to the role of CKD (raw or washed) in affecting the hydrothermal reactivity of silica sand in EI-Karnak cement pastes.

A Method for Semi-quantitative Analysis of C-S-H Gel in a Blended Cement Paste

An amended method for accurate measuring the quantity of calcium silicate hydrate(C-S-H) in pure cement paste and blended cement paste by water adsorption was made, which based on R.A.Olson’s method. Two improvements to this method, such as using C-S-H gel by hydro-thermal synthesis as standard sample and the stoichiometry of C-S-H gel is partitioned based on hydration time and the amount of mineral admixture. The result of C-S-H gel content in pure cement paste and blended cement paste is higher than by R.A.Olson’s method.

Mechanical Properties and Microstructure of Blended Cement Containing Modified Quartz Tailing

The amount of inert quartz tailing used in concrete construction is limited due to the low strength development of cementitious materials that may be caused by the quartz tailing. We manage to increase the strength of blended cement by modifying quartz tailing through solid-phase reaction of quartz tailing with carbide slag at high temperature. The mineral composition and morphology of the modified quartz tailing were examined by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The mechanical properties and microstructure of blended cement mortars containing modified quartz tailing were investigated. Results showed that the strengths of blended cement mortars containing modified quartz tailing were close to those of the corresponding blended cement mortars containing quartz tailing at early age of 3 d, but increased significantly to be similar to that of plain Portland cement mortars at late ages of 90 d. This is attributed to the microstructure densification and the enhancement of interface between quartz tailing and cement paste due to the hydration of b-C_2 S surface layer on modified quartz tailing.

Early Hydration of Composite Cement with Thermal Activated Coal Gangue

Composite cement samples were prepared by mixing clinker, gypsum with burnt coal gangues which was calcined at various temperatures. The mechanical strength and Ca（OH）2 content in the cement paste were tested, and the paste composition and microstructure were analyzed by thermogravimetry-differential thermal analysis （TG-DSC）, X-ray diffraction（XRD）, scanning electronic microscopy （SEM） and pore structure analysis. Results demonstrate that the thermal activated coal gangue could accelerate the early hydration of cement clinker obviously, which promotes the gangue hydration itself. The early hydrated products of the cement are C-S-H gel, Ca（OH）2 and AFt. The cement with 30% （in mass） the gangue exhibits higher mechanical strength, and among all the cement samples the one with the gangue burnt at 700 ℃ displays the highest hydration rate, mechanical strength, the most gel pores and the lowest total porosity.

SIMULATION OF CEMENT-PASTE SETTING BEHAVIOR BASED ON THE PHYSICAL PROPERTIES OF BLENDED-CEMENT POWDERS

In this study, an empirical model was developed to simulate the setting process of cement pastes, with and without limestone. Interestingly, an excellent linear correla­tion was found between the time required for the cement pastes to reach penetra­tion depths of 0 mm to 40 mm (the setting process) and the physical properties of the powders comprising those pastes. The empirical model was based on this clear, linear behavior, determined by means of linear regression analysis. The developed model offers an easy way to predict and to control the setting history of any cement paste, with and without limestone additive, by simply using the available, measured physical properties of the blended cements with limestone particles of various sizes.

Formulation Design of the Multi-component Cement Additive by Using Engineering Statistics

A novel methodology for the formulation design of the multi-component cement additive for the low early strength blend cement was presented by using engineering statistics.Components of cement additive such as triethanolamine,chloride,saccharide and a kind of divalent alcohol were simultaneously tested according to the arrangement of response surface methodology.Mathematical models were established to express the quantitative relationship between the chemical components of cement additive and the compressive strength of treated blend cement.The effectiveness and the possible interactions of these four chemicals contributing to the strength development of blend cement were further explored by the pareto chart and the contour plot.Finally according the performance analysis of four chemicals,the optimized formulations were brought forward and were validated in practical trials by Turkey＇s multiple comparison.

Hydration process in Portland cement blended with activated coal gangue

This paper deals with the hydration of a blend of Portland cement and activated coal gangue in order to determine the relationship between the degree of hydration and compressive strength development.The hydration process was investigated by various means:isothermal calorimetry,thermal analysis,non-evaporable water measurement,and X-ray diffraction analysis.The results show that the activated coal gangue is a pozzolanic material that contributes to the hydration of the cement blend.The pozzolanic reaction occurs over a period of between 7 and 90 d,consuming portlandite and forming both crystal hydrates and ill-crystallized calcium silicate hydrates.These hydrates are similar to those found in pure Portland cement.The results show that if activated coal gangue is substituted for cement at up to 30%(w/w),it does not significantly affect the final compressive strength of the blend.A long-term compressive strength improvement can in fact be achieved by using activated coal gangue as a sup-plementary cementing material.The relationship between compressive strength and degree of hydration for both pure Portland cement and blended cement can be described with the same equation.However,the parameters are different since blended cement produces fewer calcium silicate hydrates than pure Portland cement at the same degree of hydration.

Effect of temperature on the hydration process and strength development in blends of Portland cement and activated coal gangue or fly ash

This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process,pore structure variation,and compressive strength development of activated coal gangue-cement blend(ACGC) . Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method,thermal analysis,mercury intrusion porosimetry,and mechanical testing. To evaluate the specific effect of activated coal gangue(ACG) as a supplementary cementing material(SCM) ,a fly ash-cement blend(FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs,increasing the degree of hydration of the cement blends,and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C,but when the curing temperature reaches 60 °C,the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.

RE-USE OF SPENT CATALYST FROM OIL-CRACKING REFINERIES AS SUPPLEMENTARY CEMENTING MATERIAL

Advanced technological achievements and the continuous growth of economy have made the disposal, recycle and reuse of industrial by-products a severe challenge. The cement industry is considered one of the key sectors in this effort in successfully （in terms of not extenuating but improving some of the properties of the final product） absorbing large quantities of solid wastes, either as aggregates or as secondary cementitious materials. This not only contributes to the creation of an energy and CO2-emission depository （as commonly used raw materials are spared）, but also simultaneously alleviates the acute environmental burden caused by the irresponsible disposal of such by-products. In this study, the possibility of reusing spent fluid catalytic-cracking catalyst （FCC） as a supplementary cementing material （SCM） was examined. A series of tests were conducted, initially aiming at characterizing the material and thereafter evaluating its pozzolanic activity and its effect on the mechanical properties of blended cements. Major findings in this investigation revealed that the use of FCC as a mineral admixture in cement is feasible, strengthening the belief that siliceous glassy residues should represent a steady supply for the construction sector.

Extending blending proportions of ordinary Portland cement and calcium sulfoaluminate cement blends:Its effects on setting,workability,and strength development

This study extended blending proportion range of ordinary Portland cement(OPC)and calcium sulfoaluminate(CSA)cement blends,and investigated effects of proportions on setting time,workability,and strength development of OPC-CSA blend-based mixtures.Thermogravimetric analysis(TGA)and X-ray diffraction(XRD)were conducted to help understand the performance of OPC-CSA blend-based mixtures.The setting time of the OPC-CSA blends was extended,and the workability was improved with increase of OPC content.Although the early-age strength decreased with increase of OPC content,the strength development was still very fast when the OPC content was lower than 60%due to the rapid formation and accumulation of ettringite.At 2 h,the OPC-CSA blend-based mortars with OPC contents of 0%,20%,40%,and 60%achieved the unconfined compressive strength(UCS)of 17.5,13.9,9.6,and 5.0 MPa,respectively.The OPC content had a negligible influence on long-term strength.At 90 d,the average UCS of the OPC-CSA blend-based mortars was 39.2±1.7 MPa.