Optimization of mechanical performance, shrinkage, and environmental impact of slag-based geopolymer mortars with CKD and glass powder using response surface methodology

This study investigates the optimization of self-compacting mortar (SCM) properties incorporating cement kiln dust (CKD) and glass powder (GP) as partial replacements for ordinary Portland cement (OPC). Slump, flow, compressive strength, flexural strength, and porosity were studied by central composite design (CDD) to investigate the impact of CKD and GP (0–25% each). Material variability was understood using statistical models developed from SCM property prediction (R2 = 0.92–0.95). In the case of CKD, the workability generally increased, whereas the workability decreased in the case of GP, especially at the higher levels. Both materials reduced compressive and flexural strengths, with CKD being the most significant contributor. Higher CKD and GP contents increased porosity, proportional to strength losses. The optimum formulation of 7.22% CKD and 5.26% GP, which showed the highest desirability of 0.97, was identified as the optimum formulation with a balance between fresh and hardened properties through the desirability approach. The optimized mixture resulted in a slump (22.98 cm), flow time (11.55 secs), compressive strength (54.33 MPa), flexural strength (8.4 MPa), and porosity (14.49%). The optimized formulation demonstrates significant environmental and economic benefits, reducing CO₂ emissions by 68.15 kgCO₂/t (12.39%) and decreasing material costs by $5/ton (12.4%) compared to the control SCM. This study demonstrates the possibility of integrating CKD and GP in SCM, offering a sustainable alternative to traditional cement-based mortars without significant performance loss.

In many parts of the world, fine grained soils are regarded as one of the major concerns for civil engineering projects. To mitigate these problems, fine grained soils are typically replaced with stronger materials. However, due to the high cost of this approach, various researchers have tried alternative approaches, the most popular of which is soil stabilization. This method could be deemed suitable for pavements. The research focuses on stabilizing fine soil through the utilization of cement kiln dust (CKD) and ground granulated blast slag (GGBS). This research involves treating fine soil with 10% of the total binder consist from (GGBS+CKD), with the amount of GGBS to CKD determined by dry soil weight as follows: (10% GGBS + 0% CKD), (8% GGBS + 2% CKD), (6% GGBS + 4% CKD), (2% GGBS + 8% CKD), and (0% GGBS + 10% CKD). The compaction parameters, consistency limitations, and the findings of the Unconfined Compressive Strength (UCS) test were used to assess the enhancement levels. In addition, specimens were subjected to UCS testing after (7-28) days of curing. The findings demonstrated that the combination of GGBS activated by CKD notably enhanced the physical characteristics of fine soil. The Plasticity Index (PI) decreased from 7.4 for untreated soil to 4.8 for a mixture containing 10% binder, comprised of 2% GGBS and 8% CKD, and to 4.25 for a single-binder mixture with 10% CKD. Furthermore, the unconfined compressive strength test (UCS) results indicated that a 10% binder mixture of 8% GGBS and 2% CKD increased the UCS by 2.9 to 5.9 times compared to untreated soil after 7-28 days of curing.

Synergistic alkali activation of cement kiln dust and ground granulated blast furnace slag: Material performance and reaction kinetics.

Concrete technology involves nowadays several types of chemical admixtures. One of them is set and hardening accelerating admixtures. Main benefits of their usage are enhancement of early compressive strength and shortening of initial setting time. Unfortunately, they may cause decrease of long-term compressive strength and adversely influence durability properties of concrete. Slag blended cements with 30% and 60% of slag content were used. Ground granulated blast furnace slag (GGBFS) that is main non-clinker constituent of those cements is beneficially changing its properties. It favourably affecting long-term compressive strength, consistency and durability properties of concrete. Main drawback of slag blended cements are decrease of early compressive strength and extension of initial setting time. Both accelerating admixtures and ground granulated blast furnace slag have advantages and disadvantages that may be at least partially balanced. Slag blended cements were composed in laboratory conditions of three Portland clinkers, differing in phase composition, anhydrite as set regulating constituent and ground granulated blast furnace slag in amount of 30% and 60% of Portland clinker mass. Cements was modified with accelerating admixtures with crystal seeds and calcium nitrate as active agent and cement kiln dust in amount of 10% of the cements mass. During previous research crystal seeds and calcium nitrate were examined with CEM I, CEM II/B-S and CEM III/A, B, manufactured by one of polish cement plants. Calcium nitrate acts mainly on dicalcium and tricalcium silicate (C2S and C3S). Crystal seeds are acting physically on all cements phases by means of acceleration of C-S-H phase formation by faster crystallisation. Their performance may be similar independently on cement phase composition. Aim of this paper is to describe effectiveness of those admixtures in cooperation with CEM II/B and CEM III/A, differing in phase composition. Additionally, cements were modified with Cement Kiln Dust (CKD) and their properties were tested. Such dusts may accelerate setting and hardening of cement because of chloride and carbonate content, which are constituents of accelerating admixtures. In addition, their form of very fine powder may allow them to act similarly to crystal seeds. Initial setting time, consistency and compressive strength of mortars were examined. Tests were conducted in temperature of 20°C. Compressive strength was tested after 12, 24, 48 hours and 7, 28 and 90 days of curing in temperature 20°C in water. In most works those properties are considered separately. In order to determine efficiency of substances mentioned above the multiple-criteria decision analysis (MCDA) was made for every kind of cement. This kind of analysis allows to take examined properties as set of properties and give information about the behaviour of admixture and cement cooperation in more general terms. Criteria were defined on the basis of conducted tests and their weights were evaluated with pair analysis method. Admixture with crystal seeds was most efficient one, while Cement Kiln Dust was the least efficient.

Modern concrete technology includes mineral additives and chemical admixtures usage. It is caused by their beneficial influence on properties of concrete mix and hardened concrete. Accelerating admixtures for concrete are commonly used for shortening of time demanded for demoulding and repeat use of forms in precast facilities. They allow to conduct works during low-temperature season. Main advantage of accelerating admixtures is enhancement of early strength of concrete. Alas they may cause decrease of long-term strength and durability of concrete or increase its shrinkage One of the most popular mineral additives is ground granulated blast furnace slag (GGBFS). It is non-clinker main constituent of CEM II, CEM III and CEM V. GGBFS may be also used as additive with latent hydraulic properties for concrete. GGBFS as constituent of concrete increases consistency, long-term strength and durability, and decreases hydration heat evolution. Early compressive strength of concrete with GGBFS is lower than for Portland cement concrete. Accelerating admixtures and ground granulated blast furnace slag show advantages and disadvantages that can be equalized. In early terms calcium nitrate and crystal seeds enhanced compressive strength. Their efficiency is similar. Cement kiln dust also caused increase of compressive strength but not as much as former ones. Sodium hydroxide caused great increase of compressive strength after 12 hours but not in longer terms. In case of cements rich with C3A the compressive strength in early stage of hardening is shaped by C-S-H phase and well-developed ettringite crystal skeleton. In spite of minor differences in non-modified and calcium nitrate modified cement pastes microstructure, the compressive strength of calcium nitrate modified mortars is significantly greater in comparison to non-modified ones. The greatest compressive strength was achieved by mortar modified with crystal seeds. Responsible for this increase is more well-developed C-S-H phase. Mortars modified with sodium hydroxide are weaker after 2 days of curing in comparison to non-modified mortar. It is caused by sparse ettringite crystal skeleton. Microstructures of non-modified and modified with cement kiln dust (CKD) cement pastes are similar. It is connected with similarity of chemical composition of CKD and Portland clinker. The compressive strength of CKD modified mortars is slightly greater than non-modified one.

산업부산물인 고로슬래그 미분말 및 플라이애시를 적용하였던 선행 연구들과 차별하여 시멘트 킬른 더스트, 실리카퓸, 규사미분말 등의 기타 산업부산물을 사용한 알칼리 활성 무시멘트 모르타르의 품질특성을 검토하고자 하였으며, 그 결과는 다음과 같다. SF 치환의 경우 Plain에 비해 유동성이 저하되었으나 강도발현에는 우수한 경향을 나타내었으며, CKD와 SP의 사용량 증가에 따라 각각 유동성 및 압축강도가 증가하였다. 유동성 증진 및 초기강도 향상에 각 결합재의 고유입도분포와 높은 상관관계를 가지는데, 이는 입자사이즈가 큰 BS 및 FA 입자사이에 입자가 작은 CKD, SF 및 SP가 공극을 충진하여 연속입도곡선을 형성하는 것에 기인한 것으로 사료된다. BS 기반 조기강도 증진용 알칼리 활성 모르타르의 초기강도 향상 및 유동성 개선을 위해서는 고유의 입도분포를 가진 기타 결합재를 치환 사용하는 것이 효과적인 것으로 판단된다. This study investigated quality properties of alkali activated cement free mortar using industrial by-product such as cement kiln dust(CKD), silica fume(SF) and quartz sand powder(SP) to compare with previous research about blast furnace slag(BS) and fly ash(FA). The results were as following. All materials were effective to increase compressive strength, however they showed different tendency on flowability. CKD and SP increased flowability, but on the other hand SF did not because it's blain was great difference with other materials. Flowability and compressive strength were related with grading distributions of binders because CKD, SP and SF which had small particle size filled up BS and FA. Application of industrial by-products with various grading distributions could be effective for the high early strength and flowability of alkali activated cement free mortar using BS.

Soft soil concerns, due to high compressibility and low bearing capacity, prompted an investigation into stabilizing clay soil. Traditionally, binder including cement or lime has been used as stabilizers though a current requirement of alternatives is stem from environmental concerns. The study focused on the viability of using a novel binary activated blended binder composed of environmentally friendly materials, namely ground granulated blast furnace slag (GGBS) activated by cement kiln dust (CKD). The experimental work included investigating the impact of the developed binders on the Atterberg limits, standard Proctor compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), and field-emission scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy. CBR tests were conducted after 7 days of curing or soaking, while UCS and SEM analyses were conducted after 7 and 28 days of curing. A fixed binder ratio of 9% was maintained, with GGBS blended at 25%, 50%, and 75% with CKD. For comparison, samples of untreated and treated soils with unary binders from GGBS and CKD were also prepared. Results indicated that activated binders notably decreased soil plasticity and maximum dry density, while elevating optimum moisture content, CBR, and UCS, especially in later stages of treated soil and unary GGBS binder. Unary CKD binder exhibited a similar trend to activated binders. The activating of 25% GGBS with 75% CKD provided the optimum binder which increased the mechanical strengths by about 6 times than untreated soil. SEM revealed substantial formations of C-S-H and C-A-H gel, along with ettringite, intensifying with time. This research provides viable outcomes for stabilizing clay soil using environmentally friendly binders, demonstrating significant improvements in soil properties, particularly when using the binary activated blended binder consisting of GGBS and CKD.Graphical

본 연구에서는 실무에서 주로 사용되고 있는 FA, 35 및 CKD 치환률에 따른 콘크리트의 기초적 물성 및 건조수축에 미치는 영향을 분석하고 이를 토대로 건조수축 해석을 실시하여 혼화재가 콘크리트의 건조수축에 미치는 영향을 정량적으로 평가하고자 한다. 실험변수로서 혼화재 치환률은 <TEX>$0{\sim}20%$</TEX> 수준으로 결정하였고, W/B는 <TEX>$40{\sim}50%$</TEX>의 수준으로 결정하였다. 건조수축해석을 위해 지수함수모델을 적용하였다. 연구결과에 따르면, 혼화재 치환율이 증가함에 따라 유동성 및 공기량이 감소하였으며 초기압축 강도가 저하됨을 확인 하였다. 건조수축 특성으로 혼화재 치환률이 증가함에 따라 건조수축은 증가하는 경향을 보였으며, 건조수축 해석결과 지수함수 모델이 측정치를 양호하게 추정함을 알 수 있었고, 혼화재의 영향을 고려할 필요성이 제기되었다. In this paper, the engineering properties and estimation of drying shrinkage of concrete incorporating fly ash (FA), blast furnace slag (BS) and cement kiln dust (CKD) were discussed. FA, BS and CKD contents ranged from 0% to 20%. Water to binder ratio (W/B) also ranged from 40 to 50 %, with a 5% interval. For estimating drying shrinkage, an exponential model proposed by the author was applied, According to results, the use of FA, BS and CKD resulted in a decrease of flowability and air contents. As expected, the use of admixtures also decreases the early age strength of concrete, while at later age, due to a pozzolanic reaction of FA and BS, the compressive strength was recovered to a value comparable with that of plain concrete. For drying shrinkage, the use of admixtures led to an increase in the drying shrinkage of concrete. The exponential model suggested by the author showed good agreement between the calculated and experimental values both at early age and at later age.

Concrete pavements are integral to sustainable infrastructure, offering longevity and resilience in construction and transportation. This study focuses on optimizing concrete pavements through the incorporation of steel and carbon fibers with Ground Granulated Blast Furnace Slag (GGBS) to enhance mechanical strength, reduce fracture development, and minimize carbon emissions. Utilizing 25 mixing designs with a consistent water-to-cement ratio of 0.40, varying ratios of GGBS, steel fibers, and carbon fibers (0.5 %, 1 %, and 1.5 % based on concrete volume) were explored. A comprehensive evaluation, including slump, compressive strength, flexural strength, split tensile strength, water absorption, abrasion resistance tests, carbon dioxide emissions, and cost analysis, was conducted at different curing stages. Results revealed a decline in compressive strength for all mix designs at 28 days, attributed to reduced cement strength with GGBS substitution. The 1.5 % steel fiber and 50 % GGBS mix demonstrated minimal compressive strength reduction (30.1 MPa, 5.5 % less than control), outperforming other mixtures. Steel fibers surpassed carbon fibers, likely due to \\erior distribution. Notably, 1.5 % steel fibers showed superior results, particularly with 50 % GGBS. Compressive strength generally increased with GGBS content, except for 1 % fibrous samples where 40 % GGBS produced optimal results. At 90 days, compressive strength increased for most designs, with G50S1.5 exhibiting over 38 % growth compared to the control. Steel fiber-containing samples outperformed carbon fiber-containing ones, showcasing the efficacy of steel fibers in enhancing compressive strength. Split tensile strength generally decreased, but steel fibers improved it, emphasizing their positive influence. Flexural strength increased in 28 and 90 days, with steel fiber-containing designs outperforming. G30S1.5 showed the most significant increase (33.3 %) at 28 days, and G30S1.5 exhibited the highest growth (32.22 %) at 90 days. Abrasion resistance tests indicated steel fibers and GGBS positively impacted abrasion reduction. G50S1.5 demonstrated the highest abrasion resistance (25 % increase over control). The environmental evaluation revealed lower CO2 emissions for GGBS-containing designs. G50S0.5 showed a 40.34 % reduction compared to the control sample. Cost analysis showed GGBS reduced costs, but fiber addition, particularly carbon fibers, increased costs. G30C1.5 had the highest cost increase (208.5 %), while G50S1.5 showed a marginal rise (3.9 %) compared to the control. Therefore, steel fibers in concrete pavements offer improved mechanical properties, durability, and reduced environmental impact, making them a viable choice despite a slight increase in cost. Conversely, carbon fibers are cautioned against due to their higher cost and inferior mechanical properties.

The global demand for environmentally sustainable and cost-effective materials that reduce carbon emissions and energy consumption has significantly risen. In this context, geopolymer binders, primarily sourced from industrial by-products or agricultural waste, have emerged as viable alternatives to traditional Ordinary Portland Cement (OPC). This study examines the characteristics and microstructure of two types of geopolymer mortars: one utilizing an alumina-rich binder, namely calcined clay, and the other employing a silica-rich binder, namely rice husk ash. Both mortar types incorporate a consistent 30% Ground Granulated Blast Furnace Slag (GGBFS), with Calcined Dolomite Powder (CDP) added in varying proportions of 10%, 15%, 20%, and 25%. A total of eight geopolymer mortar mixes, along with a reference mix consisting of 100% OPC, were prepared and evaluated for setting time, flowability, compressive strength, flexural strength, and dry density. Additionally, microstructural analysis was conducted using electron microscopy techniques. The results indicated that the clay-based geopolymer mortars outperformed those based on rice husk ash. Notably, the mixes containing 30% GGBFS, 50% calcined clay, and 20% calcined dolomite powder, as well as those with 30% GGBFS, 45% calcined clay, and 25% calcined dolomite powder, exhibited performance levels comparable to, or slightly exceeding, those of the reference mix.

Abstract: With the exponential growth of industrialization, industrial by-products are also increasing day by day. One of the byproducts of the steel industry is ground granulated blast furnace slag (GGBS). In addition, GGBS is a good cement mortar due to its durability and strength, and glass waste is a waste material that can replace cement. After 28 days, the pozzolanic reaction between cement hydration and glass powder showed that cement replacement did not affect the compressive strength of concrete. The use of GGBS and waste glass powder (WGP) is the focus of this article. In this experiment, slag (GGBS) and mineral additive (WGP) were used instead of cement by weight. To examine the differences in concrete properties, the differences between glass powder and GGBS were added to the cement. The results regarding air entrainment were compared with partial replacement of glass powder and GGBS. We examined the strength of concrete with the addition of WGP (5%, 10%, 15%, 20%&amp; 25%) to the M40 mixture. Additional cement can be replaced with additional materials such as 40 with GGBS (5%, 10%, 15%and 20% weight cement) at the desired WGP percentage change. Splitting tensile strength, flexural strength and compressive strength tests were conducted. The tests showed that the combination with one sample had better effect than the combination model.

This paper presents a laboratory study on the use of cement kiln dust (CKD) as an activator of fly ash when used in high volumes within concrete. Two separate batches of fly ash and CKD were tested to assess the effect of material variability on binder properties and compressive strength gain. Ternary blends of fly ash (55–65%), CEM 1 (30%) and CKD (5–15%) and quaternary blends that included moderate amounts (15–18·5%) of ground granulated blast-furnace slag (GGBS) were prepared. Physico-chemical properties of individual binder materials were compared and concrete compressive strength was measured at 2 d, 7 d and 28 d. Ternary blends of 60% fly ash, 30% cement and 10% CKD resulted in moderate early age and 28 d strength and addition of GGBS enhanced strength significantly due to increased ettringite formation. Particle fineness, water demand and loss on ignition content of fly ash, and calcium oxide and sulfur trioxide content of CKD were found to be the main physico-chemical factors that influence compressive strength gain.

Nowadays, with increased demand for aggregates for concrete and an awareness of the need of protecting natural resources, experts are becoming increasingly interested in waste material as a building material substitute. However, the compressive strength is influenced by the composition of concrete. In this study, the compressive strength of concrete under substitution using waste from cockle shells and glass was investigated using Response Surface Methodology (RSM). Central Composite Design (CCD) based on RSM was used to assess the influence of epoxy resin, cockle shells powder, and glass powder on compressive strength responses. RSM developed first-order and second-order mathematical models with findings from experimental design. Analysis of variance was used to determine the correctness of CCD's mathematical models. Desirability analysis was then employed to optimize epoxy resin, cockle shells powder, and glass powder yielding maximum compressive strength. The RSM analysis revealed that the empirical results fit well into linear and quadratic models of concrete compressive strength. The mixing components will produce cement with compressive strength in each formulation of 54.71 MPa (4.88% epoxy resin and 4.0% cockle shells powder), 47.82 MPa (6.85% epoxy resin and 8.0% glass powder), 147.0 MPa, (4% cockle shells powder and 8% glass powder), and 56.08 MPa (4.4% epoxy resin, 4.0% cockle shells powder, and 8.0% glass powder). The results confirmed that a reasonable compressive strength of concrete could be achieved using epoxy resin, cockle shells powder, and glass powder.

Utilization of cement kiln dust (CKD) with its high alkali content in the activation of geopolymer specimens to create nonconventional cementitious binders was investigated. Relatively high alkaline content of CKD is predominant factor preventing its recycling in cement manufacture. It was observed that depending on the water-soluble alkalis and sulfate compounds, CKD could provide the necessary environment to activate geopolymer materials. Materials used in this investigation are ground granulated blast furnace slag (GGBFS), air cooled slag (ACS), cement kiln dust (CKD) and calcined kaolin. Calcinations process was done by kaolin firing at 750°C for 3 hours. Alkaline activation by 2% NaOH along with the added cement dust was studied as compared with that not activated by sodium hydroxide. Curing was performed at 38°C under 100% relative humidity. Results showed that 25% CKD is the optimum ratio for geopolymer formation and activation of ggbfs by 2% NaOH along with 25% CKD results in best enhancement in mechanical as well as microstructural characteristics. Activation of low iron metakaolin by 50% CKD and 2% NaOH has the lowest mechanical properties due to calcium deficiency that bind geopolymer matrix. Effect of 5% magnesium sulfate on alkali activated water cooled slag and metakaolin (high iron content) by cement kiln dust results in an enhancement in their mechanical properties up to three months, while subjected to a strength loss up to six months.

Properties of blastfurnace cements (CEM III/A, B, C) based on Portland cement clinker, blastfurnace slag and cement kiln dusts