Chapelle Test Research Articles

Novel utilization of waste concrete powder in alkali-activated binder

This experimental study investigates a novel approach to utilize waste concrete powder (WCP) in conjunction with metakaolin as a precursor in the production of alkali-activated binder for sustainable consumption of construction and demolition waste. A Chapelle test confirms the presence of reactive silica in thermo-mechanically activated WCP. Different alkali-activated mixtures with metakaolin replacement ranging from 0 % to 80 % were prepared. The mixture with 40 % activated WCP, with a sodium silicate to sodium hydroxide ratio of 2, achieved better compressive strength than the reference sample without WCP. Mineralogical analysis of the mixture pastes revealed that activated WCP-based mixtures developed geopolymer gel and C-S-H gel, contributing to better strength properties in the case of the mixture with 40 % activated WCP. Life cycle analysis demonstrated that incorporating 40 % thermo-mechanically activated WCP by replacing metakaolin reduces carbon dioxide emissions by 49.5 % and 2.2 % compared to Portland cement and metakaolin-based binder, respectively.

Biochar Enriched Concrete for Carbon Sequestration

Abstract: In upcoming years , a lot of construction is going to happen leading to more cement consumption and more GHG’s emissions by default as an embodied carbon. Reduction of cement consumption is possible by partially repacing it with biochar which is a by-product of pyrolysis of biomass or adding it as an additive in cement mortar and concrete for carbon sequestration. Biochar is effective in carbon sequestration activity and results in high water and carbon dioxide holding capacity. Increase in biochar lead to increase in carbon sequestration . As pozzolanic activity lead to strength gaining characteristics and durability of concrete, this study focusses on investigating pozzolanic activity of biochar. Biomass considered in this study were walnut shells and pretreatment was done with 0.1 N HCl and and pozzolanic activity is checked by chapelle test by observing Ca(OH)2 fixation during the titration. It was observed that increase in temperature or Normality of HCl in pretreatment does not enhance pozzolanic activity of biochar . Hence pretreatment with 0.1 N HCl at room temperature for an hour is sufficient to enhance the pozzolanic activity of biochar with much high carbon dioxide sorption as compared to usual concrete without compromising with the strength of concrete. This study reclaims the potential use of biochar in concrete is reliable for carbon sequestration.

Study on Sugarcane Bagasse Biochar in Concrete for Carbon Sequestration

Abstract: Embodied carbon from manufacturing of cement is increasing day by day as constructions are happening everywhere so the consumption of cement is increasing by default. In next decade there are much more constructions are going to takes place that will lead to Increase in GHG’s emissions from cement manufacturing. It is supposed to be a threat to climate . To reduce this increase in embodied carbon there is need to reduce cement consumption by partially replacing cement with other suitable options. biochar which is a by-product of pyrolysis of biomass and is effective in carbon sequestration activity and results in high water and carbon dioxide holding capacity. In this study Sugarcane bagasse biochar is used in concrete and mortar as partial replacement of cement for carbon sequestration. Strength characteristics of materials are supposed to be interlinked with pozzolanic activity hence pretreatment is done with 0.1 N HCl to enhance pozzolanic property activity of biochar. This pozzolanic activity is calculated by considering Ca(OH)2 fixation during the titration in chapelle test. From the study results its is observed that pretreatment with 0.1 N HCl at room temperature is sufficient to increase the pozzolanic activity of biochar also this Sugarcane bagasse biochar is observed to be sequestering carbon dioxide and it is increasing with increase in biochar. But compressive strength of concrete is decreasing with increase in sugarcane bagasse biochar. Hence it is not suitable to be used in construction work but can be used in plaster mortar where no much compressive strength is required . Sugarcane bagasse biochar can act as carbon sequestering media in concrete but it can’t be recommended in concrete or mortar for construction work.

Using ceramic demolition wastes for CO2-reduced cement production

This study focuses on assessing the pozzolanic potential of two types of ceramic demolition waste, namely terracotta roof tiles and sanitary porcelain, as substitutes for traditional calcined clays in blended and limestone calcined clay (LC3) cement production. Experimental methods employed include the modified Chapelle test and XRD for pozzolanic activity evaluation, flexural and compressive strength tests, capillary absorption measurements, and SEM for microstructure analysis. Mortars containing 10%, 20%, and 30% ceramic powders and 5%, 10%, or 15% limestone filler were tested. The findings showed that porcelain powders exhibited lower pozzolanic activity due to their lower surface area and higher firing temperature of the material. Up to 20% substitution of OPC with terracotta had minimal strength impact, with a 103% strength activity index (SAI) at 90 days. Ultrafine terracotta powder showed promise in LC3 production with up to 30% OPC substitution, achieving a 97% SAI after 90 days. The poor mechanical properties of porcelain-containing mortars were explained by surfactants present in sanitary porcelain. This research informs the cement and processing industries on the potential use of specific ceramic demolition waste materials in eco-cement production, offering insights into blended pozzolanic cements and LC3 formulations, with the goal of reducing the carbon footprint of cement manufacturing.

Dosagem de argamassas de alta resistência ecoeficientes otimizadas pelo modelo de empacotamento compressível

Abstract The production of eco-efficient cement-based materials is essential to reduce CO2 emissions from the construction industry. A substantial reduction in global CO2 emissions can be achieved by using clinker in mortar and concrete more efficiently and using low-CO2 minerals as partial replacements for Portland cement. However, the proportioning of eco-efficient composites is complex and the reduction in clinker content may affect its properties. This paper aims to optimize the mix design of high-strength mortars containing supplementary cementitious materials (limestone filler, fly ash, metakaolin, silica fume). The compressible packing model associated with a simplex mixture design were used together with chemical parameters, to limit the amount of active SCMs for the model iterations. The results show a significant decrease in the environmental impact of the mortars, which presented compressive strengths between 76 and 118 MPa at 91 days and binder indexes between 10 and 15 kg/m3/MPa. The reactivity of the SCMs (based on the modified Chapelle test) were successfully used to establish the Portland cement substitution (up to 13%), preventing the presence of unreacted SCMs and optimizing the use of limestone filler and sand, which have a lower environmental impact. The high-performance blends reached 8.73 kg CO2e/MPa, up to a 30% reduction in CO2e emissions compared to the mortar with only Portland cement.

Pozzolanic activity of stockpile ash: Comparison of test methods

The paper deals with the determination of the pozzolanic activity of coal-fired power plant fly and bottom ash deposited in stockpiles in the Czech Republic. The pozzolanic activity of the ash was determined using the Frattini test, modified Chapelle test, electrical conductivity test, and strength activity index. The ash collected from a stockpile was not found to display any pozzolanic activity by the methods utilised. However, milling the fly and bottom ash was shown to be the means of activating its pozzolanic properties. The study demonstrated the pozzolanic activity of the deposited ash notably increasing together with a growing time of milling and the associated increase in the specific surface area. Also, the research study presented here carried out the comparison of the individual methods regarding their effect on the pozzolanic activity and has revealed their good mutual correlation.

Developing mortar using limestone flash-calcined dredged sediment/millstone-clay cement binder (LFC)

This study aims to develop a sustainable cement binder that resembles limestone calcined clay cement by examining the effects of flash calcination on the physical and mineralogical properties of materials, and their potential as pozzolanic material. The study will evaluate whether flash-calcined material, made from marine sediments or excavated clayey soils at 750 °C, can be a substitute for metakaolin (MK), commonly used to enhance cementitious formulations. The researchers aim to determine whether the flash-calcined material can achieve similar properties to MK when developing mortar made of limestone flash-calcined sediment/millstone-clay cement (LFC). The study shows that flash calcination improves pozzolanic reactivity by enhancing BET surface area and density without altering chemical characteristics. The Chapelle test confirms pozzolanic reactivity in the flash-calcined sediment (FCS) and flash-calcined millstone clay (FCMC), and physical, mechanical, and microstructural tests are conducted to analyze their impact on various formulations of mortar and paste samples. The results suggest that LFC with MK, FCS, and FCMC can achieve better strength than the reference mix C0. Microstructural tests demonstrate that mortar designed with FCS and FCMC have similar compositions to that with MK.

Fine demolition wastes as Supplementary cementitious materials for CO2 reduced cement production

Construction and demolition waste accounts for a significant amount of the total solid waste produced worldwide, and its recycling is challenging. Although some demolition waste is processed into recycled sand and rubble, the finer fractions resulting from screening and washing of recycled aggregates are not used. This research investigates the potential of use of real demolition wastes, namely concrete screening fines (CS), mixed concrete-ceramic screening fines (MS), and mud from recycled aggregates washing (WM), as supplementary cementitious materials (SCMs) in eco-efficient blended cement. The study employed various experimental methods, such as isothermal calorimetry, thermogravimetric analysis (TGA), and setting time tests, to evaluate the hydraulic activity of waste materials and the Chapelle test and TGA to assess their pozzolanic activity. The mechanical properties and microstructure of mortars containing 20% of waste powders were evaluated using compressive strength tests and scanning electron microscopy (SEM). The results showed that thermal treatment of waste materials at 500 °C improved the mechanical properties of mortars, increasing Strength Activity Index (SAI) by 10% for CS and MS and by 6% for WM after 90 days of curing. All three waste types achieved similar mechanical properties, with compressive strengths of at least 37.93 MPa, 46.25 MPa, and 51.33 MPa after 7, 28, and 90 days of curing, respectively. The contribution of waste powders to mortar strength was due to filler effect and partially dehydrated C-S-H products. However, pozzolanic ceramic inclusions in waste powders did not affect mortar strength at a 20% substitution rate. Therefore, the research findings indicate that waste materials derived from demolition can potentially be used as environmentally friendly materials in construction. Their use as SCMs with a substitution rate of 20% can reduce the CO2 emissions of cement production by at least 10.7%.

Reactivity of raw, pyroprocessed and GGBS-blended alum sludge (AS) waste for sustainable cement production

This paper investigates AS waste to produce a construction binder of low environmental impact. It studies the reactivity of AS so that it can be used instead of traditional (higher impact) binders. Currently, most construction binders are Portland cement (PC) based, hence carrying a major environmental impact. Significant impact can be offset by using wastes as binders. Alum sludge (AS) waste is massively produced in drinking water plants, and its primary component is aluminium hydroxide (Al(OH)3). Both the raw and the calcined AS exhibit pozzolanic activity measured by the Chapelle test. The organic matter in raw AS inhibits pozzolanic reaction and hydrate formation, hence the raw AS specimens display low strength. Calcination removed the organic matter and induced the dehydroxylation of Al tetrahedra thereby increasing the pozzolanic activity of AS. The AS burned at 450 and 600 °C shows excessive reactivity which results in a flash set. However, at 800 °C, some amorphous Al(OH)3 transforms into semi-amorphous γ-Al2O3 avoiding flash set and allowing handling while maintaining significant reactivity that yields substantial strength. At 1000 °C, the conversion of amorphous Al(OH)3 into inert corundum significantly lowers reactivity. Therefore, pyroprocessing AS at 800 °C produces material of high reactivity: abundant calcium aluminate hydrates were evident in the pastes due to pozzolanic reaction and secondary hydration involving CO32− ions. Replacing 50% 800°C-AS with GGBS enhances strength and avoids strength reduction (caused by the conversion of carbonate AFm phases to Si-rich AFm phases, possibly stratlingite). A blend of 800°C-calcined AS and GGBS, in a lime or PC system, renders workable setting times and a high ultimate strength. Calcination is the key parameter affecting AS as binder replacement. When incorporated into lime or PC systems, improper calcination may cause problems such as flash setting and a strength reduction.

Effect of thermo-mechanical activation of waste concrete powder (WCP) on the characteristics of cement mixtures

The objective of present study is to utilize and study the reactivity and hydration behaviour of thermo-mechanically activated waste concrete powder (WCP). For activation, the WCP was burned for 2 h at 650 °C, followed by mechanical grinding through ball milling. The reactivity of the activated WCP was improved significantly, as corroborated through the Chapelle test, hydration analysis and compressive strength analysis. Different blends were prepared with 10 to 40 % OPC replacement. Activated WCP was found to be effective in enhancing the reactivity of cement mixtures for all replacement proportions and developed comparable compressive strength in comparison to OPC. At 56 days, the application of activated WCP resulted in the developed of 75.5 % better compressive strength than the application of as received WCP. Mineralogical analysis exhibited the development of more secondary C-S-H gel with the formation of calcite at the later age. Using lifecycle analysis software, the replacement of 40 wt% of OPC with activated WCP was calculated with 37.6 %, 39.8 % and 19.7 % less CO2 emissions, less mineral resources consumption and less energy consumption, respectively.

Thermo-chemico-mechanical activation of bagasse ash to develop geopolymer based cold-pressed block

• Sugarcane bagasse ash (BA) is used as precursor to develop geopolymer brick. • Reactivity of BA was assessed, and its semi-dry paste was thermo-chemcio-mechanically activated. • Dune sand and river sand was used to further enhance the strength. • Good physico-mechanical relationships have been obtained and results are aligned with ASTM specifications. • FTIR analysis reconfirm the results and strengthen the discussion at molecular level. Sugarcane bagasse ash (SCBA) is an agricultural waste, and it is well recognized as pozzolanic material after calcination. However, it’s potential to be used as precursor in geopolymerization; in raw form, after calcination or chemical treatment, along with the cold pressing is not being investigated in depth. Therefore, this experimental work was designed in which initially, the reactivity of SCBA was assessed by a modified Chapelle test, TGA, and XRD analysis. And later a paste was formed by mixing FA with different dosage of SCBA (10–30 wt%) in an alkaline environment and then further activated mechanically. Afterwards dune sand, another industrially discarded material, was also mixed to formulate mortar and to get benefits of its natural fineness. For mechanical activation, 20 MPa molding pressure was applied and a reduction in strength was observed by increasing SCBA contents. Whereas an increase in strength was observed when calcined SCBA was used (thermo-mechanical activation). The 20 % SCBA has almost the same results under both activation modes and therefore this percentage was selected for mortar formulation and a further increase in strength (up to 73 %) was observed. The strength gain mechanism was discussed at the molecular level by conducting FTIR analysis. Among all techniques, the mechanical activation and incorporation of dune sand was found to be the best choice. Furthermore, the physico-mechanical relationship was established, and the developed block was compared with the fired clay brick. It was observed that developed block has a lower density (1600 kg/m 3 ), lower water absorption (less than 15 %), and more strength than the limit specified (10.7 MPa) by ASTM standards. Moreover, by incorporating sand the strength criterion (21.3 MPa) for severe weathering condition was also achieved.

Novel approach to synthesize clay-based geopolymer brick: Optimizing molding pressure and precursors’ proportioning

A novel approach has been proposed to synthesize clay-based geopolymer brick; series of experiments have been performed and three mandatory steps have been evolved. In Step-1, the reactivity of fly ash (FA) and clay was assessed through the modified Chapelle test. In Step-2, a semi-dry mixture of geopolymer paste was prepared and cylindrical specimens were formulated at molding pressures from 0 to 60 MPa at intervals of 10 MPa. And in Step-3, FA and clay contents were varied from 25 to 75% to form geopolymer paste, and specimens were prepared at two molding pressures (20 and 40 MPa), which is based on the results of Step-2. Physico-mechanical performance of specimens, cast in Step-2 and Step-3, was evaluated, and compared, and the rate of geopolymerization and microstructure was assessed through FTIR and SEM analysis, respectively. From the results, it was revealed that both precursors, clay and FA, were reactive, and molding pressure increases the wettability of both materials and resulted in an increase in compressive strength and density, and a decrease in porosity and water absorption. The amount of clay is attribute to the strength gain at high molding pressure due to its crystallinity load-bearing capacity and chemical surface compatibility with cementing properties of reactive mass. The strength gain mechanism was discussed at the micro-level as well as the molecular level. Finally, the proposed approach was validated by synthesizing the brick at the pilot scale. The physico-mechanical properties of brick were compared with the codes and cylindrical specimens, a close correspondence was observed between them, and also fulfil the criteria mentioned in standards.

Mechanical and durability properties of biochar concrete

Cement production, which now accounts for over 7% of global CO2 emissions, could be a major roadblock to the Paris Agreement's goal of net-zero emissions by 2050. Greenhouse gas emissions during cement production arise from the processing of clinker where a large amount of fossil fuel is burnt for energy generation, and the remaining part comes from the energy it takes to get to the necessary high temperatures. Partial replacement of cement by residuals from agricultural industries is one of the key strategies to mitigate CO2 emissions and help promote sustainability. The objective of the present research work is to investigate biochar, prepared by pyrolyzing rice husk (RH) at 550 °C, as an alternate supplementary cementitious material (SCM). The physical and chemical properties of biochar were characterized using elemental analysis, scanning electron microscopy, thermogravimetric, and energy-dispersive X-ray spectroscopy. Compressive strength, flexural strength, water loss, permeability, and resistance to sulfate attack tests were used to investigate the mechanical and durability features of concrete containing varied concentrations of biochar. Chapelle test was conducted to determine the pozzolanic activity of the biochar. The results indicate that concrete containing 4% biochar improved compressive strength by 2.32%, flexural strength by 23.52%, and durability by 17.3% because the finer biochar particles have a packing effect resulting in the formation of a dense matrix.

Characterization of the Omni-Processor Sewage Sludge Ash for Reuse as Construction Material

Omni Processors (OP) are machines which use sludge as a fuel to generate electricity and clean water, but create ash at the same time. In the present study, fly ash and bottom ash are investigated as materials for potential reuse in the construction field. First, the granular size, density and Blaine finesse are determined. Then, the chemical composition and microstructure are obtained by means of X-ray fluorescence and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), respectively. Finally, ashes reactivity is determined by two chemical methods (modified Chapelle test, bound water content R3) and a mechanical method (pozzolanic activity index). The characterization results indicate two material types: fly ash similar to cement and bottom ash similar to fine sand. That’s why the mortars mechanical strength with fly ash 0%-30% is better than that with bottom ash at the same rate. Fly ash slightly decreases the mechanical strength of mortars while bottom ash induces a much more significant decrease.

Effects of kaolin characteristics on the mechanical properties of alkali-activated binders

The present study examines the potential use of six Kaolin samples collected from different deposits to produce calcined kaolin-based alkali-activated binders. The samples were initially characterized to assess their chemical compositions and reactivity through x-ray fluorescence (XRF), x-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and Chapelle-test. Mortar specimens were prepared for measuring the hydraulic activity as well as the compressive strength. The chemical analysis of the Kaolin showed a wide range of Al2O3 content (7.4–28.9 wt%), whereas the difference in the SiO2 was minor. Chapelle test results reflected the quality of the Kaolin used in this investigation, with values ranging from 350 to 700 mg/g. All Kaolin samples exhibited clay-based crystalline compounds that disappeared after calcination and converted to amorphous phases. A wide range of compressive strength values was obtained for the resultant alkali-activated binder (15–40 MPa) at 90 days. Direct correlations were found between calcined kaolin characteristics and the 90-days compressive strength of the alkali-activated binder. Kaolin samples with high pozzolanicity and higher Si/Al ratio were found to be more pronounced to produce alkali-activated binder with higher compressive strength values. Higher Fe and Al contents in the calcined Kaolin were found to lower the compressive strength of the alkali-activated binder.

Comminution: A Supplementation for Pozzolanic Adaptation of Sugarcane Bagasse Ash

Sugarcane bagasse ash (SCBA) has commendable potential as pozzolanic material on account of silica as an attractive oxide composition; however, the coarser size of SCBA fractions hinders the fullest potential. In this regard, the choice of the comminution process is inevitable. In the present investigation, three sugarcane bagasse ash samples with a variable loss on ignition (less than 20%), but in compliance with the oxide composition requirement of ASTM C618, were selected to assess the effect of grinding on the particle size of SCBA and, in turn, the pozzolanic reactivity of ground SCBA. Four different methods of pozzolanic reactivity were adopted to evaluate the suitable characteristics of SCBA, enhancing the pozzolanicity. The results of the pozzolanic reactivity of ground SCBA showed that a particle size (D50) lower than 35 μm and particles below 45 μm higher than 60% was a desirable level of grinding in attaining the minimum strength activity index (SAI) (75%). The provided amorphous silica was more than 25%, and oxide composition conformed to ASTM C618. Assessment of the pozzolanic reactivity of SCBA through simple and feasible techniques like the Frattini test and the modified Chapelle test with SAI appears reassuring. The attainment of the suggested level of particle sizes for SCBA through comminution indicates it is a viable method for developing pozzolanic reactivity.

Use of clay from a local source for calcination and subsequent preparation of the mixed cement

This paper deals with the use of calcinated clay and micronized limestone as supplementary cementitious materials (SMCs) for preparation of blended Portland cement CEM II/B-M (Q-LL). Clay used in this study was calcinated at 700°C and pozzolanic activity after calcination was assessed using accelerated R3 pozzolanic test and modified Chapelle test. The influence of calcinated clay and limestone addition on mechanical properties and hydration process was investigated and an optimal ratio for 35% clinker replacement was found. Initial decrease of mechanical strength at early ages, caused by SCM addition, was almost compensated during maturation of the binder.

Chemo-physico-mechanical characteristics of high-strength alkali-activated mortar containing non-traditional supplementary cementitious materials

The effect of non-traditional cement replacement materials as a replacement in the ground granulated blast furnace slag (GGBS) - fly ash (FA) based alkali-activated mortar (AAM) was investigated. In AAM, GGBS was replaced with 20%, 30% and 40% of palm oil fuel ash (POFA), treated palm oil fuel ash (TPOFA), palm oil clinker powder (POCP) and bottom ash (BA) by weight. Microstructure of mortar was investigated using X-ray Diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Scanning electron microscopy (SEM). The significant parameters investigated include the microstructures, alkali-activated material's reactivity, setting behavior and mechanical properties following ASTM standard. The potential of the pozzolanic binder materials was evaluated from the Chapelle test. The results indicated that among all the non-traditional SCMs, TPOFA achieved a satisfactory performance in all the investigations conducted. In case of AAM, 30% replacement of GGBS with TPOFA attained the highest 28-day compressive strength of 82.45 MPa. The formation of C–A–S–H gel was identified in GGBS based AAM. The results obtained from this study revealed that the TPOFA based AAM can be consider as a novel alternative sustainable green and environmental friendly material. In addition, the use of 30% of pozzolanic cementitious material can be used to replace GGBS in the development of AAM to develop high strength AAM in the range of 60–100 MPa.

Pozzolanic and Cementing Activity of Raw and Pyro-Processed Saudi Arabian Red Mud (RM) Waste

This paper investigates the composition, properties and reactivity of a red mud waste generated in Saudi Arabia with a view to find alternative materials to replace construction binders of high environmental impact. The phase transformation triggered by the sintering of the RM up to 1000°C is determined with thermal and X-Ray Diffraction analyses. Reactivity is investigated with chemical and physical methods including the Chapelle test, setting times, mechanical index and microscopy. The RM is clearly pozzolanic, and its activity is mainly due to the reaction of feldespathoids and the formation of zeolitic and feldspathoid-based hydrates. The positive effects of the thermal treatment are seen below 750°C, and include the loss of water in the zeolite/feldespathoids, and the destruction of the crystal structures of the clay minerals inherited form the parent bauxite. The negative effects of the thermal treatment are evidenced over 750°C, with a decrease in specific surface area, devitrification and crystal formation, whereby the active transition aluminas and the fedespathoids/zeolites (mainly cancrinite) transform into nepheline, tricalcium aluminate (C3A) and gehlenite. Despite the occurrence of nepheline, C3A and gehlenite in the RM sintered at 1000°C, the formation of pozzolanic hydrates that cause setting and strength development are greater at lower temperature. The optimum thermal treatment that enhances pozzolanic activity lies at c.400°C, as evidenced by the highest lime combination, the greatest mechanical index and the fastest set. The RM consists of gibbsite and boehmite, inherited from the bauxite, and cancrinite, chantalite and sodalite formed during the Bayer process. Feldespathoids have formed, instead of zeolites, due to the available silica and the high alkali content of the RM. The quick lime -CaO -, added twice during the refining process, has transformed the original goethite into hematite, and produced cancrinite. The Saudi RM has high SiO2 and high alkalinity, and an abundant specific surface area available for reaction. The chloride and carbon contents are low, and no environmental toxicity is inferred from its chemistry.

Investigation of particle characteristics and enhancing the pozzolanic activity of diatomite by grinding

This study aimed to assess the influence of grinding on improving the pozzolanic activity of a low porosity diatomite. To that end, three diatomites were produced, with 50% passing particle sizes (D50) between 7 and 40 μm, and characterized based on oxide composition, loss on ignition, X-ray diffraction (XRD), particle size distribution, and gas adsorption (specific surface area and porosity). Pozzolanic activity was assessed by electrical conductivity, modified Chapelle test, mechanical testing of lime-based mortar at 7 days, and performance index with Portland cement at 28 days. Additionally, portlandite (CH) consumption by diatomite was monitored up to 91 days of hydration by XRD-Rietveld refinement measurements in CH-diatomite pastes combined with controlled calcination at 900 °C. The grinding procedure ensured effective particle size reduction and produced an ultrafine diatomite (D50 below 10 μm) with low energy consumption. The decline in particle size caused an increase in the specific surface area (SSA) of diatomite without significantly changing pore volume and size. The larger SSA raised the silica solubility and pozzolanic activity of diatomite, altering its classification in terms of pozzolanicity. As evidenced by hydration analysis, the increased reactivity and change in pozzolanicity was due to the rise in CH consumption as the SSA of the diatomite increased.