Limestone Cement Research Articles

Performance and life cycle of Portland limestone cement mixes admixed with gypsum

In this study, the life cycle and performance of normal concrete containing 35% limestone and 2% gypsum made in different ratios of water to binder (w/b) were examined. Its cost and CO2 emissions were found to be 13% and 35% lower compared to the control concrete. However, because of the greater replacement of cement with limestone filler, there is a reduction in its workability, the development of heat and strength, and the penetration resistance of water and chloride ions, especially in the early ages. The addition of gypsum marginally improved these concrete properties, but its quantity should be limited to 2% by weight of the binder. The use of gypsum beyond this limit led to a significant decrease in the properties of concrete. Anorthite, a calcium aluminosilicate mineral, was found in this concrete, and its fractured morphology was found to be more occupied with unreacted angular limestone particles. This low-carbon concrete showed an improvement in compressive strength with decreasing w/b ratios. The limestone reserve in India is abundant and spread evenly across its length and depth, and its use as the main replacement for cement in normal strength mixes would greatly reduce the impact of CO2 on the environment.

Seaweed waste in eco-friendly construction materials: Valorization of Sargassum ash as a mineral addition in fiber cements

Many coastal regions have recently faced significant challenges due to the excessive accumulation of sargassum. This genus of brown marine algae generates greenhouse gases such as methane and carbon dioxide during decomposition, as well as toxic gases such as hydrogen sulfide and ammonia. The substantial influx of these algae on shores brings far-reaching impacts on the environment, climate, health, and the economy. One way to mitigate these impacts is by using this biomass for energy production and applying the resulting ash as an alternative material in the construction industry. As such, this study aims to analyze the feasibility of sargassum ash as a replacement for limestone in fiber cement. This not only offers an environmentally responsible solution for its disposal, but also adds economic value to a material commonly seen as a waste. Several analyses were conducted on the physical and mechanical properties of fiber cement with varying percentages of limestone replaced by sargassum ash (0, 25, 50, 75, and 100 %), as well as its durability and Life Cycle Assessment (LCA). The fiber cement with 100 % sargassum ash exhibited a 74 % increase in specific energy compared to the fiber cement without the ash after accelerated aging. This mix design also presented better environmental performance in 15 of the 18 impact categories. The results demonstrate that ash holds potential as an alternative material in fiber cement manufacturing.

Sustainable utilization of phosphorus-rich sludge in cement composites: Multiscale evaluation and mechanistic analysis

The treatment of sludge poses challenges for resource utilization and environmental protection, and utilizing sludge as supplementary cementitious materials (SCMs) presents a viable solution. However, the phosphorus content significantly influences the cement hydration process. This study primarily investigates the feasibility of phosphorus-rich sludge (PRS) as SCMs and examines the effects of combining PRS with calcined clay on cement hydration. The research focuses on hydration heat, mechanical properties, microstructure, and durability of composites comprised of PRS, limestone, calcined clay, and ordinary Portland cement. The results indicate that PRS delays early hydration reactions, leading to a decrease in early compressive strength; after 7 days, the compressive strength is approximately 14.3 MPa (sample S20C10L15). However, over time, the strength increases to 34.1 MPa at 28 days, reflecting a 138.5 % increase compared to the 7-day compressive strength (with sample OPC exhibiting only 69.1 %). This correlates with the hydration exothermic peak occurring in the later stages and the transition of phosphorus's effect on cement hydration from inhibitory to non-inhibitory. The phosphorus in PRS partially replaces silicon atoms in C-(A)-S-H gel, forming C-S(A,P)-H gel. This process refines pore sizes within PRS cementitious materials, enhancing compressive strength over time. Early hydration inhibition and the subsequent pozzolanic reaction of PRS reduce portlandite content, which lowers carbonation durability and thermal expansion coefficient. However, the quaternary blend of PRS, limestone, calcined clay, and ordinary Portland cement demonstrates excellent mechanical properties. This study provides experimental evidence for reducing the environmental impact of PRS and exploring carbon reduction strategies in the cement industry.

Design, modelling and optimisation of ultra high-performance fibre reinforced concrete incorporating waste materials

The adoption of ultra-high-performance fibre-reinforced concrete (UHPFRC) in modern-day construction has gradually increased because of its high compressive and flexural strength at the early production ages. The UHPFRC's high initial cost discourages its production and widespread use. This cost can be reduced by incorporating waste materials in UHPFRC production. This study aims to design, model, and optimise a three-day heat-cured UHPFRC incorporating waste materials. To produce a sustainable UHPFRC mixture, this study combines rice husk ash (RHA) and recycled tire steel fibre (RTSF) as the primary waste components, with Portland limestone cement, river sand, superplasticizer, and water. The concrete is heat-cured in a hot water bath at 90 °C for 3 days, resulting in rapid strength development. A D-optimal mixture design technique was used to optimise the mix proportions, and mathematical models were developed to predict the compressive and flexural strengths. The non-significant lack-of-fit results and the high values of coefficient of determination (R2) revealed the accuracy of the models in predicting the compressive and flexural strengths of the UHPFRC. The low values of standard deviation (SD) and coefficient of variation (CV) confirmed the consistency and reliability of the prediction models. A numerical optimisation revealed that it is possible to design a UHPFRC mixture with a lower cement content of 38.29% of the UHPFRC mix, resulting in a compressive strength of 117.62 MPa and a flexural strength of 36.32 MPa. The study reveals that integrating RHA and RTSF into UHPFRC can yield high-performance properties, offering innovative solutions for resource scarcity and environmental sustainability in the construction sector.

Impact of clay reactivity on the hydration of calcined clay limestone cements

The substitution of Portland cement clinker with a combination of calcium carbonate and calcined clay is a promising binder concept to lower the CO2 footprint of the cement industry due to the synergetic effect of both materials which form carbo-aluminate hydrates. In this study, the reactivity of several calcined clays was tested using the R3 test and mortar strength testing in different combinations with calcium carbonate and Portland cement. A multiple regression analysis revealed that the reactivity in the R3 test depends mainly on the amorphous Al2O3 and to a minor extent on the grain size and the MgO content. It was found that the most reactive calcined clay according to the R3 test led to no significant increase in compressive strength between 7 and 28 days. This clay also shows a slightly lower overall strength after 28 days than a calcined clay that was rated “medium reactive” according to the R3 test. The most reactive calcined clay was further investigated in a hydration study using X-ray diffraction. Based on this, a thermodynamic model was built and revealed that only a comparatively small percentage of the calcined clay reacted after 28 days.

A review on serviceability of foam concrete

In the face of the present global warming crisis, building energy conservation and emissions reduction have gained increasing attention. In the sustainable development of buildings, foam concrete has become increasingly popular in the construction industry due to its excellent thermal insulation, sound insulation and fire resistance. Foam concrete employed in buildingand construction (used as either a structural or non-structural member) must meet certain serviceability criteria. This paper reviews the serviceability of ordinary Portland cement (OPC) foam concrete, geopolymer foam concrete (GFC), sulphoaluminate cement (SAC) foam concrete, magnesium phosphate cement (MPC) foam concrete and limestone calcined clay cement (LC3) foam concrete, to include drying shrinkage, creep, thermal conductivity, water absorption and acoustic properties. Subsequently, it is proposed to change the initial curing conditions to reduce drying shrinkage, add glass fiber and basalt fiber to improve creep performance, increase heat flow direction resistance and extend the thermal conduction path to reduce thermal conductivity, control slump flow to regulate water absorption, and combine sound absorbing foam concrete with sound reflecting materials to achieve a comfortable and low noise living environment. Finally, ideas and suggestions for future work are proposed.

Ternary blended concrete strength evaluation: experimental and artificial intelligence techniques

Purpose The purpose of this study is to forecast the mechanical properties of ternary blended concrete (TBC) modified with oyster shell powder (OSP) and shea nutshell ash (SNA) using deep neural network (DNN) models. Design/methodology/approach DNN models with three hidden layers, each layer containing 5–30 nodes, were used to predict the target variables (compressive strength [CS], flexural strength [FS] and split tensile strength [STS]) for the eight input variables of concrete classes 25 and 30 MPa. The concrete samples were cured for 3–120 days. Levenberg−Marquardt's backpropagation learning technique trained the networks, and the model's precision was confirmed using the experimental data set. Findings The DNN model with a 25-node structure yielded a strong relation for training, validating and testing the input and output variables with the lowest mean squared error (MSE) and the highest correlation coefficient (R) values of 0.0099 and 99.91% for CS and 0.010 and 98.42% for FS compared to other architectures. However, the DNN model with a 20-node architecture yielded a strong correlation for STS, with the lowest MSE and the highest R values of 0.013 and 97.26%. Strong relationships were found between the developed models and raw experimental data sets, with R2 values of 99.58%, 97.85% and 97.58% for CS, FS and STS, respectively. Originality/value To the best of the authors’ knowledge, this novel research establishes the prospects of replacing SNA and OSP with Portland limestone cement (PLC) to produce TBC. In addition, predicting the CS, FS and STS of TBC modified with OSP and SNA using DNN models is original, optimizing the time, cost and quality of concrete.

Synergistic performance of microwave-activated coal gangue with limestone in low-carbon cement

This study aims to apply microwave-activated coal gangue (MCG) to develop limestone calcined clay cement (LC3). The impact of microwave activation schemes (microwave temperature and holding time) on the pozzolanic activity of coal gangue were explored. After that, LC3 cements were prepared by replacing cement clinker with limestone powder (LS) and MCG at different ratios. The uniaxial compressive strength, phase composition, microstructure, and pore structure of the MCG-based LC3 cements were analyzed. The results indicate that the maximum volcanic ash activity index is achieved when the material is microwave-activated at 800 °C with a holding time of 20 min. The MCG based LC3 cements achieve the highest strength at an MCG content of 20 % with an MCG:LS ratio of 2. Then, the response surface methodology was employed to predict the optimal mixture proportions for achieving the best strength of the material. The life cycle analysis shows that the carbon emission of the MCG-based LC3 material is 30 % lower than that of Ordinary Portland Cement. This study develops a new high-performance material with low carbon emission for construction industry.

Performance of limestone calcined clay cement (LC3) made with CO2-mineralized concrete slurry waste

Concrete slurry waste (CSW) is an under-recycled material with great potential to be substitute ordinary Portland cement (OPC) after proper treatment. In this study, dehydrated CSW (DCSW) was used to mineralize CO2 and the carbonated product was used to prepare limestone calcined clay cement (LC3). The results showed that the CaCO3 content of carbonated DCSW (CDCSW) reached ∼57.7% after mineralization for 8.5 h. During carbonation the Portlandite peak disappeared after 1.5 h, and the Mc_AFm peak disappeared after 3.5 h. The alite and belite peaks gradually diminished, with a weak diffraction remaining at 8.5 h. Replacing limestone with CDCSW led to a decrease of 14.7% in fluidity, at a plasticizer dosage of 1.3%. The compressive strength of LC3-cdcsw mortar specimens was higher than those of LC3-limestone specimens at all ages. The effective chloride diffusion coefficient of LC3-cdcsw was also promisingly small (1.08 × 10−11 m2/s). The comprehensive properties (grey correlation degree) of LC3-cdcsw were 17.82% lower than that of OPC, but 17.73% higher than that of ordinary LC3. At 28 d, the contents of monocarboaluminate for LC3-cdcsw and LC3-limestone are 11.2% and 9.5%, respectively. The fourth thermal decomposition peak of LC3 system is higher than that of OPC, and the peak intensity of LC3-cdcsw is lower than that of LC3-limestone. Our work explores the pathway of carbon sequestration in concrete slurry waste for the preparation low-carbon and durable cementitious materials.

Tension Capacity of Crushed Limestone-Cement Grout.

The feasibility of using crushed limestone instead of sand in cement grout is examined in this work. This study entails performing several tests, including the Brazilian test, the compressive strength test, and the stress-strain correlation test. The curing times used were 7, 14, and 28 days for mixtures with various proportions of cement to limestone (1:1, 1:2, and 1:4). The conventional sand-cement grout laboratory tests were prepared using a similar methodology to examine the effectiveness of the suggested substitute. The findings show that the limestone-based grout has sufficient strength, but that it is less than that of the typical sand material. The values of the tensile strength and elastic modulus were determined. A focus was made on the tensile strength and stress-strain relationship. A special laboratory set-up was used to look at the progress of failure using strain gauges fitted to the cylindrical samples both vertically and horizontally. The angular shape of the particles' ability to interlock is responsible for the material's increase in strength. According to this study, crushed limestone can be used as a substitute for sand in circumstances where sand supply is constrained. The suggested grout can be used in the shotcrete of tunnels and rock surfaces.

Calcium nitrate effectively mitigates alkali–silica reaction by surface passivation of reactive aggregates

AbstractCalcium nitrate (CN: Ca(NO3)2) has been shown to mitigate alkali–silica reaction (ASR) in concrete. Such ASR mitigation has been suggested to be on account of precipitate (i.e., barrier or passivation layer) formation‐induced dissolution inhibition of reactive/dissolving aggregate surfaces. Herein, we examine the ability of CN to mitigate ASR across two cements (Type I/II and Portland Limestone Cement), for aggregates of varying reactivity, and across different types and dosages of SCMs (supplementary cementitious materials, i.e., amorphous steel slag and Class C and Class F fly ashes). Based on expansion measurements carried out as per ASTM C1260/C1567, it is observed that CN, as a function of dosage, substantively mitigates ASR in mortar formulations across aggregate types. Careful microstructural examinations, dissolution studies, and thermodynamic calculations indicate that CN induces the formation of C–S–H, portlandite (Ca(OH)2), and calcite (CaCO3) precipitate mixtures, which form on aggregate surfaces at the expense of typical ASR gels. Such precipitates create a dissolution barrier and inhibit ASR in both SCM‐free and SCM‐containing formulations. The outcomes indicate that CN is an efficient and cost‐effective ASR mitigation additive (∼$250–$600 per tonne), particularly in a time of dwindling fly ash supplies and unaffordable lithium prices (>∼$12 000 per tonne).

Impacts of advanced metals recovery on municipal solid waste incineration bottom ash: aggregate characteristics and performance in portland limestone cement concrete

The optimization of alternative materials in concrete production continues to garner considerable attention in order to meet sustainability goals and supplement natural materials. Portland limestone cement (PLC) and municipal solid waste incineration (MSWI) bottom ash (BA) have been proposed separately as green cement and coarse aggregate supplement in low-strength concrete production, creating sustainable products and alternative disposal scenario for a waste material. This study discusses the impact of advanced ash processing techniques on aggregates and presents the performance of concrete incorporating both of these products with PLC for the first time. Two sources of MSWI BA were investigated, one as-produced (TMR) and one processed with novel advanced metals recovery (AMR). The AMR process reduced total Al content in ash compared to TMR (20,500 vs 17,000 mg/kg), though not aluminum oxide content, as the AMR process targets metallic aluminum. A composition study on both aggregates supports a reduction in ferrous and non-ferrous metals following the AMR process. All control and test mixes met 28-day compressive strength requirements (17 Mpa). Both AMR and TMR MSWI BA-amended concretes yielded compressive strengths below control specimens (no ash) ranging from 17 to 23 MPa, with little to no difference observed dependent on MSWI BA processing. The life-cycle discussion supports benefits deriving from supplementing naturally mined materials and recovering ferrous and nonferrous metals with the AMR process.

Effects of pore structure and chloride binding capacity on chloride diffusion in limestone cement paste

The limestone powder has been a preferred admixture in cement-based materials due to its abundant availability and potential to reduce carbon emission. The purpose of this study is to clarify the key influencing factors for chloride diffusion in cement paste as limestone is added. The pore structure, chloride binding capacity and chloride diffusivity of cement paste with different limestone addition and fineness were measured. The deconvolution of physically and chemically bound chloride was achieved by combining X-ray diffraction, energy dispersive spectroscopy and the Rietveld method. The results show that the addition of fine limestone increases the number of 50–100 nm pores while the coarse limestone leads to more pores in the size range of 100–1000 nm. As the limestone content increases, less chloride is bound by physical adsorption while more Friedel’s salt is formed. The effective chloride diffusivity is almost unaffected when less than 10 % fine limestone is added because of increased pore tortuosity. The changes of chloride binding capacity and chloride diffusivity are equally important for the chloride diffusion when 20 % fine limestone is added. On the other hand, the reduction of chloride resistance of cement paste containing coarse limestone is mainly due to the increase of the chloride diffusivity.

Novel sustainable steel fiber reinforced preplaced aggregate concrete incorporating Portland limestone cement

This study proposes a novel approach by adding Portland limestone cement (PLC) to preplaced aggregate steel fiber reinforced concrete (PASFRC) to create a sustainable concrete that minimizes CO2 emissions and cement manufacturing energy usage. The method involves injected a flowable grout after premixing and preplacing steel-fibers and aggregates in the formwork. This study evaluates the mechanical properties of a novel sustainable concrete that uses PLC and steel fibers. To achieve the intended objective, long and short end-hooked steel fibers of 1%, 2%, 3%, and 6% were incorporated in PASFRC. Also, Analysis of variance (ANOVA) was used to examine the data. Results indicated that PLC and higher fiber doses increased the mechanical properties of PAC. At 90 days, PASFRC mixtures containing 6% long steel fibers demonstrated superior compressive, tensile, and flexural strengths, registering the highest values of 49.8 MPa, 7.7 MPa, and 10.9 MPa, respectively and differed by 188%, 166%, and 290%, respectively from fiberless PAC. The study confirmed the suitability and effectiveness of using PLC with steel fibers in PAC which significantly improved the mechanical properties of PASFRC. This was verified through analytical analysis and new empirical equations were proposed to predict the mechanical properties of PASFRC.

Optimizing the pore structure and permeability of calcined clay limestone cement through shell powder

Limestone calcined clay cement (LC3) as a novel low-carbon cement shows potential as an OPC replacement due to its lower clinker content and excellent performance. Nevertheless, Low degree of hydration in early age resulted in high porosity impacting properties. In this study, shell powder was employed as a carbonate filler to optimize the pore structure of LC3. The results indicated that adding shell powder improved pore structure, consequently enhancing compressive strength from 35.8 MPa to 40.5 MPa at 28 day. The collaboration of shell powder with limestone led to the highest compressive strength 41.2 MPa and lowest porosity 18.4 % at 28 days. The matrix had good compatibility when limestone and shell powder are combined for LC3. With the increased content of shell powder, the volume fraction of gel pores gradually increased, and the harmful pores decreased, which promoted the transformation of pores into gel pores. Pore connectivity was reduced, resulting in a denser LC3 matrix. Therefore, shell powder was a material that can effectively improve the mechanical properties and pore structure of LC3.

Evaluation of the strength performance and microstructural properties of different based metakaolin blended cements containing greenly synthesized nanosilica

The drive towards improving the properties of cement composite thus making it eco-friendly, sustainable, and durable, has been the focus of the construction industry. Kaolin is one of the pozzolans that have been investigated in recent times, but its reactivity is influenced by its source. In addition, the problem of homogenous mixing onsite and early strength development of pozzolana blended cement are evident. This research focused on the strength and microstructural properties of factory-produced metakaolin blended cement incorporated with green nanosilica. Kaolin samples were obtained from three locations and calcinated at 700 ℃ for 1 h. Metakaolin was interground with 10% Portland Limestone Cement (PLC) clinker at the factory. Binder-sand ratio (1:3) with a water-binder ratio of 0.5 was adopted for batching the mortar. Nanosilica was added to the mortar at: 1, 2, 3, 4, and 5%, respectively. Prisms of 40 × 40 × 160 mm were cast and cured for 3, 7, 14, 28, 56, 90, 180, 270, and 365 days, respectively. The flexural and compressive strengths of prisms including the water absorption of cubes were evaluated. 10% MK addition enhanced the mechanical properties of the mortar with MK C having the highest enhancement. Incorporation of 1% nanosilica enhanced strengths at early and later ages, as well as refinement in the pores of the mortar with increasing nanosilica.

Whole-life carbon emissions of concrete mixtures considering maximum CO2 sequestration via carbonation

A comparison of cradle-to-gate embodied carbon emissions and carbon dioxide (CO2) sequestration potential due to carbonation of portland cement (PC), portland limestone cement (PLC), and limestone calcined clay cement (LC3) concrete mixtures is presented in this work. First, the cradle-to-gate embodied carbon emissions of the concrete mixtures were calculated using life cycle assessment (LCA). Then, the CO2 sequestration potential of each mixture was computed using a theoretical model for CO2 sequestration that was derived using principles of cement chemistry to account for the carbonation of both calcium hydroxide (CH) and calcium silicate hydrate (C-S-H). The results indicate that a theoretical maximum of 33 % of the cradle-to-gate embodied carbon emissions of the concrete mixtures analyzed herein can be realistically sequestered via carbonation. Data also substantiate that concrete mixtures with higher cradle-to-gate embodied carbon emissions sequester the most CO2. However, concrete mixtures with lower cradle-to-gate embodied carbon emissions, namely PLC and Type I, II, III, IV, and V mixtures with high-SCM replacements, typically yield the lowest whole-life carbon emissions. The results indicate that concrete mixtures with high SCM replacement should be prioritized—regardless of which cement is used to produce the concrete—from a whole-life carbon emissions perspective.

Quantification of critical chloride threshold of reinforcing steel embedded in portland limestone cement systems containing supplementary cementitious materials

Quantification of critical chloride threshold of reinforcing steel embedded in portland limestone cement systems containing supplementary cementitious materials

Influences of alumina type and sulfate content on hydration and physicochemical changes in Portland–limestone cement

This study explored the influence of alumina type and gypsum content on the hydration, mechanical properties, and chemical changes of Portland–limestone cement (PLC) using isothermal calorimetry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), ionic chromatography (IC), compressive strength testing, X-ray diffraction (XRD), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR) spectroscopy, and mercury intrusion porosimetry (MIP) testing. The addition of alumina shortened the induction period, accelerated the acceleration period, and increased the mechanical strength of the PLC pastes with 3 and 7 wt% gypsum. The acceleration effect and strength enhancement were not distinct in the PLC pastes with less gypsum (0.1 wt%). The addition of γ-alumina led to the greatest accelerating effect and strength improvement in the PLC pastes with 3 and 7 wt% gypsum, and the compressive strength achieved was comparable to those of pure Ordinary Portland cement (OPC) pastes without limestone. The addition of γ-alumina induced the rapid dissolution of gypsum and consumption of sulfate ions. The chemical change affected by the addition of alumina varied greatly depending on the gypsum content, and trends in AFt and AFm formation in the PLC pastes with different gypsum contents were confirmed. Finally, pore size refinement was observed through the addition of alumina to PLC pastes with 3 and 7 wt% gypsum.

Secondary durability implications: Steam cured, carbonated concrete containing limestone filler, and GGBFS

The motivation of this work is three-fold: jurisdictions are moving from general use (GU) cement to general use limestone (GUL) cement or Portland cement (PC) to Portland limestone cement (PLC); ‘carbonation curing regimes’ are being widely considered/studied/implemented; and modular construction using precast elements may achieve ‘lower carbon’ concrete infrastructure. This study aims to examine the interplay between various mix constituents (i.e. GU, GUL, limestone filler (LF), and ground granulated blast furnace slag (GGBFS)), curing regimes (atmospheric (0.04% CO2), accelerated (3% CO2) carbonation, and steam curing), and coupled environmental effects on durability of ready mix and precast concrete. In this study, the term “secondary durability implications” of carbonation processes refers to the effect of carbonation on the concrete's indicators of durability (i.e. water absorption (sorptivity), and rapid chloride permeability) and its durability (i.e. against freeze/thaw cycles and deicer scaling). The results reveal that: 1) a combination of GUL cement +10% GGBFS achieves a lower carbonation depth and a higher compressive strength than the other mix designs in the same curing regime without steam curing; 2) steam curing within 24 h of casting leads to a lower long term strength and a greater carbonation depth for a same mix design that is moist cured; and 3) secondary durability implications of (accelerated and atmospheric) carbonation cured (after 28-day moist curing) concrete for the (GUL cement + 10%GGBFS) prisms exhibit stronger resistance against 300 freeze-thaw cycles and de-icer salt scaling resistance compared to the 301-day moist cured mixes.