Clinker Aggregates Research Articles

Engineering and microstructural properties of environmentally friendly alkali-activated composites containing clinker aggregate: heat-curing regime and elevated-temperature effect

The common wisdom in the literature about clinker aggregate (CA) is that it improves the performance properties of mortar or concrete to some extent. The current study, in this context, investigated the physical characteristics and mechanical performances of alkali-activated composites (AACs) made entirely with CA. The CA was used in three particle sizes of 0–2 mm (named No.10), 2–4 mm (named No.5), and 4–8 mm (named medium). To examine the impact of the fine CA-size fraction on the characteristics of AAC, No.10 CA was partially replaced by No.5 CA up to 50%, while the content of the medium CA was kept constant in all AAC mixtures. Moreover, to evaluate the influence of the 8-h curing temperature on the performance of the AACs, different temperature-based curing strategies (ambient, 45, and 75 °C) were applied to the AACs. In the production of AACs, granulated blast furnace slag was employed as an aluminosilicate-rich raw material, and a sodium silicate and sodium hydroxide combination was used as an alkaline activator. Physical properties (flowability, water absorption, capillary water absorption, and dry unit weight), and 8-h strength performances (flexural and compressive) were determined. Furthermore, to monitor the influence of high temperatures on the characteristics of the AAC, the mixtures were exposed to elevated temperatures (200, 500, and 800 °C). In SEM image analysis, it was determined that spherical CSH gels were formed in the heat-cured AACs. It has been observed that the geopolymerization products decompose in AACs exposed to 800 °C. To evaluate statistically the experimental results, a multi-factor analysis of variance (ANOVA) was also applied. The results revealed that increasing the coarser fine aggregate fraction led to higher water absorption and apparent porosity capacities and lower unit weight. Besides, strength performance was improved by applying a heat-curing strategy to the AAC, whereas a decrease was observed by increasing the No.5 CA fraction. There was a remarkable reduction in compressive strength and considerable loss of mass when the AAC mixes were exposed to high temperatures.

Potential improvement of clinker sand in the mechanical high temperature and transport properties with GGBS-based prepacked geopolymer composite

In this study, a new generation prepacked geopolymer composite (PGC) material that can meet different needs was obtained by combining geopolymer concrete (GPC) and prepacked aggregate concrete (PAC) technology. In the production of PGC, 5-8 mm quartz aggregates were placed in molds and, geopolymer mortar was injected between these aggregates. Aluminosilicate based blast furnace slag (GBFS) was used as binding in geopolymer mortars; sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as alkali activator. In addition, clinker aggregate in different proportions was used as fine aggregate (0–4 mm) in the production of mortar. Within the scope of the study, the physical, mechanical, permeability and high temperature resistance properties of PGC were investigated. The produced samples were cured at 30 and 60 °C for 6 and 8 hours. Hardened unit weights of PGC vary between 2342 and 2539 kg/m3, and sorptivity values vary between 0 and 0.04 kg/m2.min0.5. While the increase in curing temperature and curing time increases the hardened unit weight values, it decreased permeability values. While the increase of clinker aggregate in the mortar phase does not change the hardened unit weight, it significantly reduced permeability. When the PGC samples are cured at 30 °C, the compressive strengths are 20.38–39.03 MPa; when curing at 60 °C, the compressive strengths are 35.21–57.04 MPa. Flexural strengths, 2.35–6.96 MPa with 30 °C cure, achieved 4.27–9.93 MPa results with 60 °C curing. Increasing the curing time and curing temperature significantly increased the compressive and flexural strengths. The increase in the amount of clinker aggregate added to the mortar phase decreased the strength values. While the compressive strength values of PGC mixtures do not fall below 15 MPa after being exposed to 300 °C high temperature; after the application of 600 °C high temperature, it lost up to 70% of its strength. Increasing the curing time and curing temperature, increased the high temperature resistance. The increase in the amount of clinker aggregate in the mixtures, decreased the strength loss rate.

Recycling of waste marble powder and waste colemanite in ternary-blended green geopolymer composites: Mechanical, durability and microstructural properties

The objective of this investigation was to identify the effects of curing temperature, cement clinker aggregate, waste colemanite (WCM) and waste marble powder (WMP), as well as their interaction, on the early physico-mechanical properties, microstructure, and high-temperature resistance of geopolymer composites (GC). Ground granulated blast furnace slag (GBFS), metakaolin (MK), and silica fume (SF) were employed as precursors for the production of GC. These materials were activated using a solution of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). In the fabrication of the GC, fillers such as WMP, WCM, and cement clinker aggregate (CCA) were employed. Four GC mixes were generated and cured for 8 h at curing temperatures of ambient (20 °C), 60 °C, and 90 °C. Investigations were conducted into how curing temperature, WMP, and CCA affected the GC's compressive, flexural strength, water absorption, dry unit weight, porosity, and sorptivity. The resulting mixes' performance at high temperatures was also assessed. Using SEM, microstructure investigations of GC mixes made for the study were also carried out. The obtained results indicated that the mixture M2 containing 100 kg/m3 of WMP and 750 kg/m3 of CCA exhibited the greatest compressive strength of 24.60, 55.60 and 68.80 MPa at ambient, 60 °C and 90 °C respectively compared the other GC mixtures. Moreover, the compressive strength of the M1 mixture enhanced by 190.65% and 239.56%, at 60 °C and 90 °C respectively compared to ambient-cured samples. Ambient cured mixture M4 that contains maximum WBM and minimum CCA content exhibited the strength enhancement of 54.01, 46.52 and 29.95% at 150, 350, and 550 °C respectively.

Characterization study of geopolymer concretes fabricated with clinker aggregates

Geopolymers are a new generation of building material that has recently been popular in reducing carbon emissions. As a result of its amorphous alumina-silicate-based reaction product, it has many superior properties. This study investigated the mechanical and physical properties and high-temperature resistance of ground-granulated blast furnace slag and metakaolin-based geopolymer concrete fabricated with clinker aggregates produced in a short curing time (8 h). In alkali activators, the sodium silicate to sodium hydroxide (SS/SH) mass ratios were 2, 2.25, 2.5 and 2.75. Two curing methods were used, namely ambient (25 °C) and oven curing (80 °C). The observed unit weights vary between 2275–2392 kg/m3 for the samples of the geopolymeric composites. Porosity and water absorption vary between 4.92 and 8.84% and 3.58–7.26%, respectively. The heat curing application decreased the mixtures' water absorption, unit weight, and porosity values. The compressive strength of the samples subject to ambient curing varied between 39.2 and 59.8 MPa. Withal, the samples cured at 80 °C for 8 h were between 66.9 and 112.4 MPa. The increased SS/SH ratio also increased the observed strength values. Capillary water absorption of all samples is below 0.6 kg/m2. Heat-cured geopolymers decreased capillary water absorption to 0.1 kg/m2. The weight loss after high temperature decreased as the SS/SH ratio increased. The N-A-S-H gel in the zeolitic structure was observed in SEM analysis. The FT-IR analysis visualized the carbonation in the heat-cured mixtures. As a result, over 100 MPa compressive strength values were observed with the clinker aggregates at 80 °C after 8 h of curing time. Withal, a high-temperature refractory composite was developed with the clinker aggregates. Moreover, the nuclear radiation shielding abilities of geopolymer concretes were investigated experimentally. The gamma shielding parameters of the samples were evaluated by transmission measurements in the range of 0.081–0.661 keV. Also, neutron dose measurements were performed, and the samples produced as neutron attenuator capacity was evaluated. The radiation shielding capabilities were improved slightly with increasing sodium silicate solution content.

The effect of clinker aggregate on acid resistance in prepacked geopolymers containing metakaolin and quartz powder in the presence of ground blast furnace slag

Climatic change and global warming occurred due to CO2 emitting from cement manufacturing are increasing rabidly, and attention is paid to produce and improve geopolymer concrete with waste materials (fly ash, silica fume) and by-product material (ground granulated blast furnace slag). The aim of this research is to identify the performance of geopolymer concrete containing metakaolin (MK) for 100 kg/m3, 200 kg/m3, and 250 kg/m3, and the quartz powder (QP) for 100, 200, and 300 kg/m3, as sand replacement in the presence of ground blast furnace slag GBFS in clinker prepacked geopolymers. Four groups of specimens are studied involves: two groups incorporating QP and MK cured at 45 °C, and two groups are cured at 75 °C. The physical and mechanical properties are studied at conventional conditions. Moreover, the compressive strength and the mass loss are investigated for all the mixes not only exposed to 350 °C and 700 °C, but also the samples subjected to acids; hydrochloric acid (HCl), sulphuric acid (H2SO4), and nitric acid (HNO3). The findings showed that, increasing QP content up to 300 kg/m3 has a positive effect in improving geopolymer concrete properties, for all curing regimes. Withal, the metakaolin addition, contributes significantly in the strength performance, but the optimum strength is obtained at 200 kg/m3 replacement. The samples cured at 75 °C enhanced the absorption resistance, mechanical properties, unit weight, high-temperature resistance, and acids’ reissuance, as well. A striking strength improvement was obtained for 42% and 68% quartz powder addition at 45 °C and 75 °C, respectively. Moreover, the strength is doubled for metakaolin addition at high temperature curing. The strength variations through presence of acids are also observed as prominent decrements, as expected.

Physico-mechanical and shielding properties of alkali-activated slag composites incorporating cement clinker aggregate: Effect of high temperature and particle size

The purpose of this research was to see how cement clinker aggregates (CCA) and curing temperature affected the physico-mechanical and shielding properties of alkali-activated composites (AAC) exposed to high temperature. The precursor used to create AAC was ground blast furnace slag (GBFS), which was activated using a solution of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). Quarts powder with a size range of 0–0.5 mm and CCA in two different size ranges (0–4 mm and 4–8 mm) were used as fine and coarse aggregates in the fabrication of AAC. Four different AAC mixes were produced which were cured by three curing temperatures at 25 °C (air curing), 40 °C, and 80 °C for 8 h. The impacts of curing temperature and CCA size and content were examined on the AAC's flowability, compressive strength, flexural strength, porosity, dry unit weight, and water absorption and sorptivity characteristics. The high temperature performance and shielding properties of the produced blends was also assessed. Microstructure investigations of AAC mixtures produced within the scope of the study were also carried out based on FTIR and SEM. The obtained results implied that compressive strength of up to 80.80 MPa was attained with the use of CCA at curing temperature of 80 °C. The M4 containing the highest CCA content with the sizes of 4–8 mm and the lowest CCA content with the sizes of 0–4 mm exhibited the lowest strength at all curing temperatures. All AAC mixes regardless of curing temperature lost more than 60% of their initial compressive strength after 300 °C. Finally, among the AAC mixtures, whose gamma-ray shielding properties were examined in the photon energy range of 81–661 keV and whose fast neutron dose rates were determined, 0–4 mm particle size Clinker doped M1 sample showed better nuclear shielding ability compared to other mixtures studied.

The effect of geopolymer slurries with clinker aggregates and marble waste powder on embodied energy and high-temperature resistance in prepacked concrete: ANFIS-based prediction model

As a special concrete type, the prepacked concrete is the aggregates placed in the mold beforehand and then produced by injecting the prepared slurry between the aggregate particles. Using geopolymer slurries in prepacked concrete can be a more sustainable solution. Geopolymer is an inorganic polymer produced using various industrial wastes (containing SiO2 and Al2O3) and alkaline solutions. The present work investigated the effect of geopolymer slurry on prepacked concrete's physical, mechanical, transport and environmental properties using natural coarse aggregates. Instead of clinker aggregate, 50, 100, 150 and 200 kg/m3 waste marble powder (WMP) was used in the geopolymer slurry. The produced geopolymer prepacked composites (GPC) were heated for 6 and 8 h at 40 and 70 °C. The apparent porosity of GPCs varies between 5.8 and 15.4% and their water absorption ranges between 2.8 and 9.5%. As the WMP rises, the water absorption and porosity of the GPCs increase. The hardened unit weight of all GPC samples is below 2400 kg/m3. GPC samples heat cured at 40 °C had a compressive strength of 6.6–15.9 MPa, whereas samples cured at 70 °C had a compressive strength of 21.9–45.8 MPa. As the heat curing temperature and time increased, the porosity of the GPC samples decreased and their compressive strength increased. GPC samples' capillary water absorption ranges from 0.12 to 1.6 kg/m2. The capillary void content reduced as the heat cure temperature rose. WMP was added to GPC mixes, which enhanced high-temperature resistance. In GPC mixes heated to 600 °C, the compressive strength greater than 10 MPa, was assessed. Embodied energies of GPCs vary between 4116 and 4851 MJ/kg. In addition, mixing ratios and curing properties can be determined with high accuracy with the ANFIS algorithm in GPC design. Map cracks were frequently formed in the microstructures of the samples. The carbonation products were inspected in the matrix at FT-IR analysis. As an observation, increasing the WMP content increases the high-temperature resistance of geopolymer slurries and decreases the amount of embodied energy.

Verification of the mutually complementary effect of fly ash and clinker aggregate on the strength, heat of hydration, and alkali-silica reaction

Verification of the mutually complementary effect of fly ash and clinker aggregate on the strength, heat of hydration, and alkali-silica reaction

Use of carbonated Portland cement clinkers as a reactive or non-reactive aggregate for the production of cement mortar

This study investigates the effects of carbonated cement clinker used as a fine aggregate on the strength and physicochemical properties of mortar. Cement clinkers in two different size ranges (0.15 mm–1.2 mm and 1.2 mm–5 mm) were replaced with natural fine aggregate. The cement clinkers were carbonated by natural and accelerated carbonation methods. The results demonstrated that the use of carbonated cement clinker has a positive effect on the strength properties of mortar. A physicochemical analysis showed that seven days of accelerated carbonation generated high levels of calcite on larger cement clinker aggregate materials (1.2 mm–5 mm). However, these higher amounts of carbonation products can detrimentally affect the creation of efficient bonding with the other ingredients in mortar and can consequently lower the strength of these materials compared to when smaller carbonated cement clinkers (0.15 mm–1.2 mm) are used in mortar. Fewer carbonation products provide additional nucleation sites for the hydration of cement grains. Therefore, relatively small carbonated cement clinker is preferable to large carbonated cement clinker to obtain high strength. The findings overall lead to the conclusion that carbonated cement clinker can be used as a reactive aggregate or non-reactive aggregate depending on the degree of carbonation. In both cases, the performance of cement mortar exceeds that of cement mortar containing natural sand.

Refractory concrete based on high-alumina cement and clinker aggregate

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Torsional Crack Localization in Palm Oil Clinker Concrete Using Acoustic Emission Method.

Palm oil clinker (POC) aggregates is a viable alternative to the naturally occurring sand and gravel in the manufacturing of concrete. The usage of POC aggregates assists in the reduction of solid waste and preserves the consumption of natural resources. Although researchers investigated the mechanical response of POC-containing concrete, limited research is available for its torsional behavior. In general, the torsional strength depends on the tensile strength of concrete. This research investigates the compressive, tensile, and torsional response of concrete with various ratios of POC-aggregates. Five batches of concrete were casted with POC-aggregate replacing granite at ratios of 0, 20, 40, 60, and 100%. The selection for the mixture proportions for the various batches was based on the design of experiments (DOE) methodology. The hard density, compressive strength, splitting tensile strength, and flexural strength of concrete with a 100% replacement of granite with POC-aggregates reduced by 8.80, 37.25, 30.94, and 14.31%, respectively. Furthermore, a reduction in initial and ultimate torque was observed. While cracks increased with the increase in POC-aggregates. Finally, the cracking of concrete subjected to torsional loads was monitored and characterized by acoustic emissions (AE). The results illustrate a sudden rise in AE activities during the initiation of cracks and as the ultimate cracks were developed. This was accompanied by a sudden drop in the torque/twist curve.

Sustainable mortar and concrete made from palm oil boiler clinker aggregate comprising rice husk ash and calcium bentonite: Compressive strength and durability assessment

Sustainable mortar and concrete made from palm oil boiler clinker aggregate comprising rice husk ash and calcium bentonite: Compressive strength and durability assessment

Retraction Note to: Artificial neural networks application to predict the compressive damage of lightweight geopolymer

In this work, compressive strength of lightweight geopolymers produced by fine fly ash and rice husk–bark ash together with palm oil clinker (POC) aggregates has been investigated experimentally and modeled based on artificial neural networks. Different specimens made from a mixture of fine fly ash and rice husk–bark ash with and without POC were subjected to compressive strength tests at 2, 7, and 28 days of curing. A model based on artificial neural networks for predicting the compressive strength of the specimens has been presented. To build the model, training and testing using experimental results from 144 specimens were conducted. The data used in the multilayer feed-forward neural networks models are arranged in a format of six input parameters that cover the quantity of fine POC particles, the quantity of coarse POC particles, the quantity of FA + RHBA mixture, the ratio of alkali activator to ashes mixture, the age of curing and the test trial number. According to these input parameters, in the neural networks model, the compressive strength of each specimen was predicted. The training and testing results in the neural networks model have shown a strong potential for predicting the compressive strength of the geopolymer specimens in the considered range.

Compressive strength and durability performance of mortar containing palm oil boiler clinker aggregate, rice husk ash, and calcium bentonite

The utilization of local waste by-products as a building material has attracted great attention for an environmental sustainability and become a fundamental part of sustainable construction. In this experimental research, the local palm oil industrial waste and agricultural waste are utilized for the green mortar production. To examine the compressive strength and the durability performance of the green mortar mixtures, Palm oil boiler clinker (POBC) was used as a substitution material for natural fine aggregate. An ordinary Portland cement was partially replaced by rice husk ash (RHA) and calcium bentonite (CB) in the proportion of 10%, 20%, and 30% by weight of cement. The compressive strength, water absorption, porosity, durability against sulphuric acid and sodium sulphate attacks, and microstructures of the POBC mortar mixtures were evaluated at the curing age of 7, 28, and 56 days. The experimental results revealed that the compressive strength, water absorption, porosity, and durability characteristics of POBC mortar incorporating RHA and CB were improved by long-term curing. Particularly, the 56-day POBC mortar incorporating up to 30% of RHA and 10% of CB yielded the superior durability against sulphuric acid and sodium sulphate attacks.

Retraction Note to: Fuzzy logic-based prediction of compressive strength of lightweight geopolymers

In the present work, compressive strength of lightweight inorganic polymers (geopolymers) produced by fine fly ash and rice husk–bark ash together with palm oil clinker (POC) aggregates has been investigated experimentally and modeled based on fuzzy logic. To build the model, training, validating and testing were conducted using experimental results from 144 specimens. The used data in the ANFIS models were arranged in a format of six input parameters that cover the quantity of fine POC particles, the quantity of coarse POC particles, the quantity of FA + RHBA mixture, the ratio of alkali activator to ashes mixture, the age of curing and the test trial number. According to these input parameters, in the model, the compressive strength of each specimen was predicted. The training, validating and testing results in the model have shown a strong potential for predicting the compressive strength of the geopolymer specimens in the considered range.

Effect of Palm Oil Clinker (POC) Aggregate on the Mechanical Properties of Stone Mastic Asphalt (SMA) Mixtures

Aggregate composition has a pivotal role in ensuring the quality of pavement materials. The use of waste materials to replace the aggregate composition of asphalt pavement leads to green, sustainable, and environmentally friendly construction, which ultimately preserves nature by reducing the need to harvest materials from natural sources. Using the Marshall mix design, the main objective of this paper is to investigate the effects of waste palm oil clinker (POC) as fine aggregates replacement on the properties of stone mastic asphalt (SMA) mixture. Six groups of asphalt mixtures were prepared using different percentages of palm oil clinker content (0%, 20%, 40%, 60%, 80%, and 100%). To determine the Marshall properties and select the optimum binder content, asphalt mixture samples with different percentages of asphalt binder content (5.0%, 5.5%, 6.0%, 6.5%, and 7.0%) were prepared for each group. The results showed that the palm oil clinker was appropriate for use as a fine aggregate replacement up to 100% in SMA mixture and could satisfy the mix design requirements in terms of Marshall stability, flow, quotient, and volumetric properties. However, the percentage of palm oil clinker replacement as fine aggregate has merely influenced the optimum binder content. Furthermore, there were improvements in the drain down, resilient modulus and indirect tensile fatigue performances of the SMA mixture. In conclusion, the use of POC as fine aggregates replacement in SMA mixture indicates a good potential to be commercialized in flexible pavement construction.

The analysis of the factors affecting the macrotexture of bauxite clinker aggregate gradation

In this research, influencing factors on the macrotexture of bauxite clinker aggregate gradation were analyzed and the role of aggregate in the anti-skid performance of asphalt pavement was determined. AMES road texture laser scanner was used to conduct macrotexture tests. It was found that the macrotextures of single grain size aggregates were enlarged as grain size was increased, the macrotextures of mixed grain size aggregates were enlarged as the proportion of small grain size particles was decreased and both fine aggregates and mineral powder extended aggregate structure. Meanwhile, the effect of aggregate size on the macro-structure of the pavement was greater than that of percent voids in coarse mineral aggregate in the dry rodded condition (VCA). In addition, mean texture depth (MTD) was first decreased and then increased with the increase of compaction work. Under the action of traffic load, macro-structure was fluctuated. The results of this paper provide some references for road designers to consider macrotexture in gradation design.

ENGINEERING PROPERTIES OF LIGHTWEIGHT GEOPOLYMER CONCRETE USING PALM OIL CLINKER AGGREGATE

The palm oil industry generates a significant amount of wastes which their managing has been a major environmental concern in producing countries. The utilization of these wastes as an aggregate source for concrete production will help to sanitize the environment and provides a cheaper and renewable aggregates source for construction industries. This paper presents the results of the experimental program conducted on fly-ash based geopolymer concrete containing Palm Oil Clinker Aggregate (POCA). Several geopolymer concrete mixes were prepared in which POC was used as a replacement to both fine and coarse aggregates at different percentages starting from 25% to 100%. Mix proportioning was done in accordance with ACI 211.1-91. Geopolymer concrete specimens were cast, cured at ambient conditions and tested for the slump, density, water absorption and compressive, shear and flexural strengths. Overall, the use of fly ashbased geopolymer binder and POCA can enhance the sustainability aspects in concrete production as well as produce a high strength concrete. A concrete mixture containing 100% POCA can produce a structural lightweight concrete having a compressive strength of more than 30 MPa and a density of 1821 kg/m3. The use of a geopolymer binder promotes the workability and strength of POCA concrete and reduces its water absorbability. Incorporation of POCA up to 75% did not much change the structural efficiency of the produced concrete, while it was reduced by 32% when the POCA fully replaced the natural aggregate. Nevertheless, the benefits in terms of cost, energy, and environmental savings cannot be overlooked.

Effect of Characteristics of Different Types of Bauxite Clinker on Adhesion

Based on the fact that bauxite clinker has minor thermal conductivity and better skid resistance and wear-resisting property, it can be used in HFST (high friction surface treatment) or the abrasion layer of asphalt mixture to replace or partly replace the existing aggregate. Bauxite clinker is classified into mainly six types according to different chemical composition contents. The selection of bauxite clinker as aggregate is not only for the economic value, but also for improving the adhesion between aggregate and asphalt, which has a certain blindness This study evaluated the characteristics of different types of bauxite clinker. The adhesion of different types of bauxite clinker with asphalt was evaluated by means of agitating hydrostatic adsorption method and surface free energy theory. The effect of characteristic parameters of bauxite clinker on adhesion was evaluated by grey correlation entropy analysis. The results show that Type B and D bauxite clinker aggregates have the best adhesion to asphalt. The outcome of grey entropy correlation analysis shows that the parameters which characterize the structural indexes of bauxite clinker, such as porosity, water absorption and apparent density, have the greatest effect on the adhesion. The results of study can provide some reference for the selection of bauxite clinker, which is used in different types of highway construction, and a theoretical reference for the applicability research of bauxite clinker in asphalt mixture and the improvement of skid resistance and durability of pavement.

Calcium-aluminate mortars at high temperatures: Overcoming adverse conversion effects using clinker aggregates

The effect of elevated temperatures on a calcium aluminate mortar with clinker aggregates is the subject of this paper. After an exposure period of 3 h at temperatures ranging from 25 to 1000 °C, specimens were tested in residual conditions in order to evaluate changes on the mechanical and microstructural properties. A simplified hydration model based on the chemical reactions of the principal minerals is proposed to predict the evolution of matrix composition from the early-age hydration. The improvement of the mechanical properties occurring due to the conversion reactions between 25 °C and 200 °C, is attributed to an increased hydration reaction of both cement and clinker aggregate. Furthermore, when compared to the metastable reactions, an improved interlocking effect at the reactive aggregate interface, and a more dense nature of the stable hydration products, were observed. These phenomena balance the adverse effects promoted by conversion reactions on porosity and mechanical properties.