Mineralogy and geochemistry of pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain monogenetic volcanoes in the central part of the Cameroon Volcanic Line

Pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain,3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line(the Tombel Plain,Bamileke Plateau,and Noun Plain),were explored in order to constrain their petrology and make some predictions on their pozzolanicity.The rocks in this study include alkaline and subalkaline basalts,trachybasalts,and basanites.Most of these rocks present an overall composition that overlaps with primitive mantle,suggesting rapid ascent of magmas,limited crustal contamination and crystal fractionation of olivine,clinopyroxene,and feldspar.The pozzolans present enrichment of LREE relative to HREE and high chondrite normalized ratios of La/Yb and Tb/Yb.ranging between 7 and 20 and>1.9 respectively,similar to those of Ocean Island Basalts.Like other nearby volcanoes,partial melting in a dominantly garnet-bearing mantle zone can be assumed.Quantitative mineralogy by X-ray diffraction revealed various mineral phases with dominantly plagioclase,augite,olivine,and Fe-Ti oxides.The samples contains important amorphous phase up to 23,51,and 69 wt%in the Tombel Plain,Noun Plain,and Bamileke Plateau,respectively.This elevated amount of amorphous phases together with the sum of SiO2,Al2O3 and total Fe2O3(SAI=68.50-83.50>70 wt%)according to ASTM C618 standard and the sum of CaO,FeO,and MgO(CIM=14.5-30.52 wt%and 23.58-31.08 wt%)suggest interesting pozzolanicity character for the studied pozzolans.

Chemical and Microstructural Effects of Different Calcinating Temperatures on Selected Pozzolans

Recent researches show that agricultural wastes can be reuse as pozolans;this contributes to our environmental sustenance. The need to successful carry out proper analysis contributes significantly to improving the overall use of the discovered pozolans. Therefore, this research aims to investigate the micro-structural and chemical analysis of some selected pozzolans at different calcinating temperatures. Rich husk ash (RHA), groundnut shell ash (GSA), locust beans pod ash (LBPA) and bamboo leaf ash (BLA) were obtained;their chemical and microstructural analysis at different calcinating temperatures (500°C, 600°C and 700°C) were carried out using X-ray fluorescence and scanning electron microscope. The results show that the optimum calcinating temperatures considering the microstructure and chemical composition of RHA, BLA and LBPA were 700°C, 500°C and 600°C respectively. These pozzolans were also classified according to ASTM 618 requirement.

Physicochemical Characteristics of Some Cameroonian Pozzolans for Use in Sustainable Cement Like Materials

In the present study, physico-chemical investigations have been carried out on the possibility of using Cameroonian volcanic or clay pozzolans as raw material for geopolymer or pozzolanic binder. The research had made some suggestive results and conclusions. Powders of less than 100 μm of five sampled pozzolans from volcanic or clay origins have been subjected to chemical and mineralogical analysis, BET specific surface, absolute density, granulometry and pozzolanic activity in solution tests. The results obtained showed that, geopolymers or pozzolanic binders can be produced from samples studied. The samples contain significant amounts of glassy or amorphous phase ready to dissolve in an alkaline solution. The high alkali content of volcanic pozzolans makes them more appropriate for geopolymer application. Clay pozzolans are the easier to grind in order to obtain the appropriate fineness and can be used for both geo- polymers and pozzolanic binders.

Valorization of Pozzolans as Partial Additive of Portland Cement: A Case of Pozzolans from the Localities of Foumbot, Penja and Tombel (Cameroon)

The objective of this study is to find alternative materials that can be used as an addition in cement in order to produce ecological and economical cement. Three pozzolans coming from different volcanic regions of Cameroon (Penja, Tombel and Foumbot) were sampling. Mechanical compressions on 40 × 40 × 160 mm3 mortar specimens were made with partial replacements of 2%, 4%, 6% and 8% of the pozzolans in Portland cement and physical analyzes on the mortar powders were carried out. The values of the activity indices of different pozzolans obtained are in the normative range. The compressive strength of motars decreases at all ages with the proportion of cement substitution. The compressive strength values up to 40 Mpa are obtained for a substitution of 6% for the pozzolans from Penja, Tombel and 8% for the pozzolan from Foumbot. Pozzolan from Foumbot which contains the highest percentage of SiO2 offers a maximum substitution rate and therefore optimally reduces the production costs of Portland cement. Physical tests show that specific surfaces increase with an additions of pozzolans from Tombel and Penja.

Optimization of the Structural Properties of RHA-Concrete Using Osadebe’s Mathematical Program

This research work focused on the analyses of the compressive strength, modulus of rupture and elasticity of RHA-concrete that was gathered from four states in Nigeria (Cross River, Ebonyi, Enugu, and Benue). The results were calculated and compared geographically by using Osadebe’s mathematical program. They had corresponding relative silica values of 85, 75, 1, 65, 2, and 60.1. In place of cement, RHA was utilized in concrete at different percentages of replacement in the concrete. The results showed that strength values increased as RHA replacement increased by 5% - 15% and decreased as the percentages of RHA in the concrete increased. When RHA is utilized to partially replace cement in concrete, the strength is improved. RHA is a yearly supply of silica and a naturally occurring pozzolan. The Compressive strength values varied between 37 and 42 N/mm2. The elastic modulus of a short cylinder obtained was between 3.15 and 3.7 N/mm2. It was discovered that the rupture modulus ranged from 0.6 to 4.2 N/mm2. Mathematical prediction models employing Osadebe’s method were created. The findings confirmed that there were differentials in the results and laboratory responses of RHA concrete based on spatial properties, Fisher’s statistical tool was used to confirm the adequacy of the model and the mean values, variance and critical values were found satisfactory for the 10 observation points.

The Effect of Wet-grinding on the Properties of Glass Powder and Its Application in Cement Based Materials

To improve the pozzolanic reactivity,waste glass(WG)needs to be micronized to fine particles so as to expedite the leaching of active constituent.The key feature of this work is to examine the effect of wet-grinded WG on the mechanical and structural properties of cement based materials.The experimental results show that wet-grinding can improve the ions leaching behavior of WGP and decrease the stability of silicon oxide bond.The pozzolanic reactivity of WGP was dramatically enhanced after wet-grinding,as high as 144.1%at 1 d and 110.9%at 28 d when the mean grain size of WGP reached 0.90μm.The ground WGP can promote the transformation of capillary pores to gel pores to improve the compactness of microstructure regardless of the reaction time.

Mechanical Properties and Durability of Sustainable Concrete Manufactured Using Ceramic Waste:A Review

Green and sustainable concrete has attracted significant attention from the construction industry and researchers since it was proposed.The ceramic waste materials are often directly buried in the ground or placed in an open dump,and the accumulation of ceramic waste contributes to environmental pollution,which makes the recycling of ceramic waste quite urgent.Owing to the pozzolanic activity,excellent mechanical properties and durability,industrial ceramic waste is considered as a suitable substitute for cement or natural aggregates to fabricate renewable concrete.In this paper,the pozzolanic activity of ceramic waste and the workability,mechanical performance,and durability of ceramic concrete are discussed.In addition,the most recent research results pertaining to ceramic concrete are reviewed.Ground ceramic powder improves the workability,compressive strength,resistance to chloride penetration,and carbonation resistance of concrete to a certain extent.Concrete containing ceramic as the aggregate has a lower mechanical performance than ordinary concrete.However,the resistance to chloride penetration,freeze-thaw resistance,and high-temperature resistance of ceramic concrete are remarkable.Ceramic concrete is environmentally friendly,requires fewer energy resources to manufacture than ordinary concrete,and has excellent engineering properties.However,further research is required for future engineering applications.

Performance Improved of a Lime and Hemp-Based Concrete through the Addition of Metakaolin

This work describes in detail the experimental investigation of the physico-mechanical properties of nonstructural hemp concrete(usually used as insulating wall material)when the Air-lime based Tradial PF70 binder is partially replaced using Metakaolin.The objective is to reduce the amount of free Ca2+ions in the binder as these are responsible for the degradation of vegetables particles and can therefore induce a loss of mechanical performances.In order to assess the effectiveness of pozzolanic reaction,amounts of 0%,10%,and 20%vol.of Air-lime binder were replaced by the Metakaolin material,while testing the mechanical properties of concrete specimens containing 200%and 300%of hemp particles.Through SEM and EDX analysis,a tight relationship has been found to exist between the Metakaolin content and physical-mechanical properties of specimen.The pozzolanic reaction consumes calcium hydroxide from binder to produce Hydrated Calcium Silicates(C-S-H)and in turn,this leads to a decrease in the pH-value of the pore solution which is the main factor responsible for hemp particle degradation.

Influence of the Partial Substitution of Industrial Clinker by Volcanic Lava Powder from Nyiragongo Volcano on the Physical Properties of Mortars

This study evaluates the pozzolanicity of Nyiragongo volcano lava flows in Congo by an indirect method using mortars with different rock powder proportions. The clinker used is a locally produced alite clinker, whose chemical and mineralogical composition was determined by XRF, Bogue and Taylor formulas. The lava flows were collected from the 2002, 2010 and 2021 eruption sites, and were characterized by XRF, CIPW normative mineralogy and geomechanical tests. The results show that Nyiragongo rocks are ultrabasic, silica- and alkali-rich, and contain minerals like nepheline, wollastonite and leucite. They satisfy the natural pozzolan criterion, and have pozzolanic activity indices above 70%. These rocks also have high RC and LA resistances, ranging from 190 MPa to 45 MPa, and from 18% to 32.6%, respectively. The rock powder addition in the mortars reduces mechanical resistances and increases setting times, except for a 5% replacement rate, which speeds up hardening. Nyiragongo lava can be used as a pozzolanic addition to produce a CEM II/B-P 32.5 cement.

Potential for Use of Iron Mining Tailings Calcined in a Flash Furnace as Pozzolanic Material

This paper presents a study of the potential use of iron mining tailings as artificial pozzolan (metakaolin) after their submission to thermal treatment via calcination in a flash furnace. The research consists of the characterization of the tailings before and after calcination, chemical, mineralogical, thermogravimetric, and mechanical strength analyses were conducted. The results were compared with those for commonly used pozzolans, metakaolin, and similarities were identified. The study of the morphology of the particles before and after calcination was conducted through analyses of images obtained by scanning electronic microscope. The pozzolanic activity of the fine mining tailings calcined with flash technology was evaluated in uniaxial compression trials, which showed excellent results.

Pozzolanic Activity of Burned Coal Gangue and Its Effects on Structure of Cement Mortar

The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions （ 20% - 60% ）. The pozzolanic activity of coal gangue burned and the hydration products were examined, the compressive strengths of the pastes of the mixtures were tested, and the mechanism of the reaction was discussed. The experimental results slum, that the coal gangue burned at 750 ℃ has the optimum pozzolanic activity, and the burned coal ganguc with SiO2 and Al2 O3 is in an active form. When the coal gangue burned at 750℃ is mixed into portland cement, the content of calcium hydroxide in paste is significantly reduced, while the contents of hydrated calcium silk.ate and hydrated calcium aluminate are increased accordingly, hence resulting in the improvement of the microstructure of mortar. The compressive strength of cement paste decreases with increasing the content of burncd coal gangue. The decease in strength is small in the range of 20% - 30% coal gangue substitution and significant in 30%- 60% substitution.

A Comparative Study on the Pozzolanic Activity between Nano-SiO_2 and Silica Fume

The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction （ XRD ） , differential scanning calorimetry （DSC）, scanning electron micrascopy （SEM） and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca（OH）2 and nano-SiO2, the reaction rate of Ca（ OH）2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca （ OH）2 with nano-SiO2 showed marked increases over those of Ca（ OH）2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca（ OH）2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.

Effect of Nano Silica on Hydration and Microstructure Characteristics of Cement High Volume Fly Ash System Under Steam Curing

The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.

Stabilization of expansive soils using chemical additives: A review

Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements.This can be achieved through chemical stabilization using additives such as lime,cement and fly ash.In this paper,suitability of such additives under various conditions and their mechanisms are reviewed in detail.It is observed that the stabilization process primarily involves hydration,cation exchange,flocculation and pozzolanic reactions.The degree of stabilization is controlled by several factors such as additive type,additive content,soil type,soil mineralogy,curing period,curing temperature,delay in compaction,pH of soil matrix,and molding water content,including presence of nano-silica,organic matter and sulfate compounds.Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction.However,presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.

Analysis of the Fractal Growth Characteristics and Nucleation Mechanism of Phosphogypsum-based Materials

Phosphogypsum-based materials (PBM) were synthesized with varied phase compositions of phosphogypsum,portland cement and fly ash.Effects of fractal growth characteristics on physicochemical properties,pore structure,compressive strength,as well as the hydration behaviour and mineralogical conversion of mortars were examined by a multitechnological approach,including mercury intrusion porosimetry,rietved phase analysis,thremal analysis,calorimetry and Fourier transforminfrared spectroscopy analysis.Expermental results indicate that the specimens cured with mosite resulted in higher strength and lower porosity compared with those cured in the drying chamber.In addition,a more complicated course of the aluminate and silicate reactions during the hydration process has been published,with the hydration products mainly consisting of calcium silicate hydrate (C-S-H),portlandite,ettringite,hemicarbonate,monocarboaluminate,calcite,quartz,a mixed AFm passed with carbonate,and hydroxide.After all,the nucleation process is a reaction that can be defined as a solid,liquid and gaseous phases that goes through the four stages of materialization mixing and modification,i e,hydration of low calcium content,secondary hydration,high calcium condensation and geoplymensation,respectively.The rupture,recombination,polymerization reactions of Si-O,Ca-O,Al-O bonds contribute to the nucleation mechanism that serves as the formation of C-S-H in hydration products.

Assessment of deterioration in RHA-concrete due to magnesium sulphate attack

The assessment of magnesium sulphate attack on concretes containing rice husk ash （RHA, 20wt% of the cementitious materials） with various average particle sizes was investigated. The total cementitious materials were 390 kg and the water-to-binder ratio （W/B） was 0.53 for all mixtures. Specimens were initially cured in water for 7 d and then immersed in the 3wt% magnesium sulphate solution for up to 111 d of exposure. The specimens were subjected to drying-wetting cycles to accelerate sulphate attack. In addition to the visual monitoring of the specimens, the concrete specimens were subsequently tested for compressive strength, dynamic modulus of elasticity, and length and mass changes. The results show that the specimens exposed to sulphate attack exhibit higher strength and dynamic modulus than those kept in water. The length change is negligible and can be attributed to the normal swelling of concrete. On the other hand, concretes suffers mass loss and surface spalling and softening; the fine RHA-concrete results in a better resistance. For the accelerated sulphate attack method used in this study, mass change and visual monitoring are recommended for assessing the deterioration degree and the effectiveness of supplementary cementitious materials to resist sulphate attack.

Rate of pozzolanic reaction of two kinds of activated coal gangue

Two kinds of activated ways are used to prepare activated coal gangue fine powder, one is calcining coal gangue at 800℃ （gangue A）, and the other is calcining coal gangue with a certain calcite at 800℃ （gangue B）. The experiment shows that strengths of blended cement mortar with coal gangue B are higher than that of blended cement with coal gangue A. Hydration of cements with the two kinds of activated coal gangue is investigated through a differential thermal analysis. The weight loss due to Ca（OH）2 decomposition of hydration products by differential thermal analysis/thermo gravimetric （DTA/TG） can be used to quantify the pozzolanic reaction. A new method based on the composition of hydration cement is proposed to determine the degree of pozzolanic reaction. The results obtained suggest that the degree of pozzolanic reaction of gangue B is faster than that of gangue A.

Using Microwave Heating to Completely Recycle Concrete

The aim of this study was to develop a technique for the complete recycling of concrete based on microwave heating of surface modification coarse aggregate (SMCA) with only inorganic materials such as cement and pozzolanic materials (silica fume, fly ash). The mechanical properties of SMCA, which was produced using original coarse aggregate (OCA) and inorganic admixtures, as well as its separation from the cement matrix and recovery performance were quantitatively assessed. The experimental results showed that micro structural reinforcement of the interfacial transition zone, which is a weak part of concrete, by coating the surface of the OCA with cement and admixtures such as pozzolanic materials can help suppress the occurrence of micro-cracks and improve the mechanical performance of the OCA. Microwave heating was observed to cause micro-cracking and hydrate decomposition. Increasing the void volume and weakening the hydrated cement paste led to the effective recovery of recycled coarse aggregate.

Assessment of Reusing Ferrochrome Slag Wastes in Mortar as SCMs

The demand for alternative cementitious materials is on the rise,as the cement causes huge energy consumption and produces greenhouse gas emission.Additionally,there is economic potential for the construction industry to reuse wastes as supplementary building materials.The purpose of this study is to evaluate the potential of utilizing ferrochrome slag wastes in mortar as supplementary cementitious materials (SCMs),thereby achieving this double-sided goal.Thus,the mechanical and physical properties of ferrochrome slag wastes were investigated to be used as admixtures in concrete production.Three different cement mortar specimens were prepared by replacing cement with ferrochrome slag in ratios of 0,30%,and 60% by mass and flexural and compressive strengths of the specimens were determined at the ages of 7,28,56,90,and 180 days.Also,the effects of the ferrochrome slag replacement ratio on workability,setting time and volume expansion were revealed.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were also investigated to study the microstructural properties of the specimens containing ferrochrome slag.Based on the results,it is concluded that ferrochrome slag wastes have pozzolanic activity,therefore reusing them as SCMs in the cement and concrete industry is convenient.

Improvising the Self-Healing Capabilities of Concrete Using Different Pozzolanic Materials and Crystalline Admixtures

To analyse the self-healing capacities in terms of mechanical performance of the pozzolanic materials,such as,fly ash,metakaolin and silica fume and crystalline admixtures.Pre-cracked concrete cubes with about 0.05 mm width were exposed to four different environmental conditions at different exposure times in order to determine the effect of temperature and water availability on the self-healing potential.After the exposure,the control and tested concrete cubes were evaluated for regained strength,void reduction,corrosion inhibition,damp proofing,relative impermeability and durability.The samples with SF10CA have better cementitious filling and low percentage of voids and water absorption.