Capillary Absorption Coefficient Research Articles

Effect of Aggregate-to-Binders Ratio on Water Resistance of Red-Mud-Modified Magnesium Phosphate Repair Mortar

The aggregate-to-binders ratio (A/Bs) is an important parameter for the design and preparation of repair mortars. In this paper, the influences of A/Bs on the physical and mechanical properties of red-mud-modified magnesium phosphate repair mortar (RMPM) were systematically investigated. By exploring the capillary absorption characteristics of RMPM, the effect mechanism of A/Bs on its water resistance and mechanical properties was further clarified. The results indicated that the fluidity of fresh RMPM reduced with an increase in A/Bs, and its setting time was first shortened and then prolonged. The compressive strength, flexural strength, interfacial bonding strength, and water resistance of RMPM increased and then decreased with the increasing A/Bs and reached the maximum when the A/Bs was 1.0. The capillary absorption of RMPM was a linear correlation with the square root of the immersion time, and whose slope, that is, the capillary absorption coefficient, and capillary porosity decreased and then increased with the increase in A/Bs. Capillary porosity had a linear relationship with the strength retention rate, which indicated that A/Bs produced a significant effect on the water resistance of RMPM by modifying its capillary pore characteristics. When the A/Bs was 1.0, RMPM had the lowest capillary absorption coefficient and capillary porosity, and thus possesses appropriate mechanical properties and water resistance.

Discussion of “Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR”

In February 2024, Construction and Building Materials published the paper “Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR”, which claims to measure the capillary absorption of moisture in brick, sandstone, mortar and concrete by means of moisture content profiling with the ‘NMR mouse’, a low-field, single-sided, open-magnet NMR instrument. This critique formulates several serious concerns on the study’s outcomes and conclusions. The excessively large similarity of the capillary absorption behaviour of the four materials is peculiar, since it disregards the differences in their open porosities and pore sizes. The overly large capillary moisture contents are equally abnormal, as they exceed the moisture storage limit of the material’s pore structure. There appears to be an inconsistency between the moisture content profiles and the overall moisture masses. Finally, it is shown that the lengthy time interval necessary for a single NMR pass limits the applicability of the NMR mouse for capillary absorption coefficients of porous building materials.

Fabricating hydrophobic silica fume to improve mechanical strength and anti-corrosion of integral hydrophobic cement mortar and its carbon emission assessment

Integral hydrophobic concrete possesses superior waterproof performance and can prevent internal concrete and steel bar from erosive ions attacking in marine environment. However, the low mechanical strength limits its application. Silica fume (SF) and stearic acid (SA) were used to prepare hydrophobic SF by ball milling. Further, the prepared hydrophobic SF was added to cement mortar to fabricate integral hydrophobic cement mortar. Effects of hydrophobic SF on compressive strength, water resistance and anti-corrosion performance of integral hydrophobic cement mortar were investigated. Besides, the cement hydration products and morphology were analyzed after the addition of hydrophobic SF. The results showed the compressive strength of integral hydrophobic cement mortar reached 48.3 MPa. The contact angle of integral hydrophobic cement mortar surface arrived 151.5–152.7°. The capillary absorption coefficient also reduced by 93.06 %–93.67 % compared with the control group. Electrochemical test results showed the integral hydrophobic cement mortar provided a long-term protection for the embedded steel bar. The hydrophobicity and pozzolanic effect of the hydrophobic SF made cement mortar a high strength, good water resistance and corrosion resistance. Additionally, the global warming potential (GWP) of hydrophobic cement mortar was calculated based on life cycle assessment (LCA). It showed that the GWP and environmental impacts of hydrophobic cement mortar reduced.

Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR

Capillarity has an important effect on the durability of buildings, and the capillary absorption coefficient is a key parameter to describe the strength of material capillarity. Most of the methods currently used to measure the capillary absorption coefficient of materials can damage the sample or are not accurate enough and need to be improved. This paper proposes a method to measure the capillary absorption coefficient of brick, sandstone, mortar and concrete by using a single-sided nuclear magnetic resonance (NMR) technique, which has the advantages of accuracy, nondestructiveness, continuity and rapidity. The relative error of the capillary absorption coefficient obtained from three repetitions of the experiment ranges from 0 to 5.11%, which is in the range of 0.64%∼1.30% compared with that obtained by the partial impregnation method. This method has great potential for application in in situ testing. This paper also analyzed the water transport behaviors in porous building materials based on the variation in NMR signal intensity in the measured materials and established a water transport model. The model is divided into two stages: the first stage is mainly the one-dimensional rise in moisture in the vertical direction. The second stage is mainly the diffusion of moisture in the horizontal direction, which continuously fills each pore space to saturation. Difficulty in removing air leads to a reduced rate of water absorption in the second stage.

Performance degradation mechanism of adobe materials under freeze-thaw cycles based on moisture transportation characteristics and microstructural analysis

It is well known that the mechanical properties and appearance of adobe materials degrade significantly during freeze-thaw cycles due to the unique moisture absorption characteristics of soil particles. In order to clarify the performance degradation mechanism of adobe materials under freeze-thaw cycles, the evolution law of the pore structure, attack products, and capillary absorption characteristics were systematically studied when experiencing 10, 20, and 30 freeze-thaw cycles. The results showed that the flocculent hydration product around the Yellow River sediments and aggregate particles gradually reduced during adobe materials subjected to freeze-thaw cycles. Volume expansion caused by the growth of ettringite in macropores and cracks led to the deterioration in pore structure and more water participated in the subsequent freeze-thaw cycles. The porosity and pore volume of adobe materials increased with the increasing of freeze-thaw cycles, and the harmful pores of 50–200 nm rose significantly. After 20 freeze-thaw cycles, harmful pores accounted for 62.3% of the total pore volume of adobe materials, which induced an enlarged moisture transport capacity, and thus the capillary absorption coefficient increased by 18.52 g/(m2·s1/2). As a combined result of above factors, after 30 freeze-thaw cycles, the loss rates in mass and compressive strength of adobe materials were 6.2% and 15.4%, respectively.

Influência da absorção capilar e da rugosidade de substratos cerâmicos na resistência de aderência de pastas cimentícias

Abstrac This study assesses the joint influence of capillary absorption and substrate roughness on the adhesive strength of a cementitious matrix on brick substrate. One cementitious rendering and two substrates with different water absorption and roughness were used. The capillary absorption coefficient and the roughness coefficient were determined in 1cm2 test areas to then evaluate the matrix tensile bond strength and correlate it with the properties of the substrates. The results were validated by SEM and AFM analyses. Substrates with higher capillary absorption and lower roughness presented higher tensile bond strength. Micro and nanoscale analyses led us to conclude that, in the substrates used, the higher capillary absorption and the lower roughness generate a denser and less porous paste-substrate interface, suggesting a higher extent of contact between the hydrated paste and the substrate and, consequently, higher adhesive strength.

Hygrothermal and strength properties of cement mortars containing cenospheres

This study characterizes the hygrothermal and microstructural properties of cement composites containing aluminosilicate cenospheres. It involved the preparation of six mortar mixtures based on CEM I 42.5R cement, in which cenospheres accounted for 0 to 100 % of the aggregate content. The research included measurements of thermal properties, compressive and bending strength tests, density tests on the cured mortars, determination of pore distribution and total porosity, and qualitative assessment of the cenosphere-cement matrix contact zone. However, the main emphasis was on moisture-related parameters. The publication discusses the effect of using cenospheres as a substitute for natural sand on water absorption, capillary absorption, and the sorption and desorption of water by the tested composites, along with the influence of individual microstructural properties on moisture properties. The results showed that increasing the amount of cenospheres added as a sand substitute contributed to an increase in the water absorption of the composite and in parallel reduction in the capillary rise coefficient. The increase in the content of cenospheres caused also a clear increase in the sorption capacity of mortars. Moreover as the statistically average distances between the pores decreased, the thermal conductivity of the composites also decreased. Both when considering the porosity and the spacing factor, the conductivity decrease with wet composites was faster than with dry ones. With decreasing distances between the pores, the compressive strength also decreased significantly. Higher content of cenospheres also reduced the density of the composite and at the same time, increased the specific surface area, which contributed to the reduction in the capillary absorption coefficient and the increase in the durability of the entire composite. In addition, relatively good insulating properties of these composites (λ as low as 0.25 W/mK) in comparison to ordinary cement-based mortars make them interesting alternative to traditional solutions, while the appropriate mechanical strength (compressive strength in the range of 37.68 to 17.74 MPa) makes them suitable even for use as structural elements.

Utilizing waste geopolymer powder as partial cement replacement for sustainable cement mortar: Micro-macro properties and modification

The increasing application of alkali-activated geopolymer materials generates more geopolymer waste, but the reuse of geopolymer waste has been given less consideration until now. The ground waste geopolymer powder (WGP) has the potential to be used as supplementary cementitious material. Therefore, this study examined the characteristics of cement-based materials with WGP as a substitute for particle cement. The mortar samples (70.7 × 70.7 × 70.7 mm) were prepared for strength and transport properties measurement. The findings indicated that WGP ground from various geopolymer wastes mainly contained C–(N)–A–S–H, mullite, SiO2 or CaCO3. Substituting WGP for partial cement negatively impacted the paste micro-structure and increased the percentages of harmful and more harmful pores. The addition of WGP reduced the mechanical strength and increased the transport properties, and the maximum capillary absorption coefficient of 30% WGP mixed mortar was 154.0% higher than that of reference mortar without WGP. When WGP replacing level was the same, the water absorption of mortar incorporating WGP ground from FA-based geopolymer waste was obviously lower than that of mortar with WGP ground from GGBS-based geopolymer waste, because WGP ground from FA-based geopolymer waste contained some un-treated FA particles which benefited filler effect and pozzolanic activity. The addition of active admixtures could enhance the performance of WGP blended mortar. Specifically, the mortar containing 20% WGP and 10% silica fume/metakaolin had similar strength and lower transport properties compared with reference mortar, and the properties of WGP blended mortar were improved with the mix of Nano-SiO2.

Experimental and numerical analysis of the hygric performance of earthen buildings after façade hydrophobization treatment

Earth is used extensively for buildings worldwide, as its thermal properties contribute to a favorable indoor thermal environment. However, earthen materials are sensitive to moisture ingress, which can result in structural damage and undesirable indoor humidity conditions. Through hydrophobization treatment, the capillarity of earth can be significantly reduced while hygroscopicity remains largely unchanged, thereby possibly improving the hygric performance of earthen buildings. In the present study, experiments and simulations were conducted to investigate the effect of hydrophobization on earthen materials and buildings. The experimental results show that the bulk density, open porosity, and pore-size distribution of rammed earth changed by only a few percent after hydrophobization treatment. The thermal properties (thermal conductivity, specific heat capacity, solar reflectivity and longwave emissivity) and hygroscopic properties (sorption isotherm and water vapor permeability) also showed limited changes (<20 % in most cases). In contrast, capillarity, represented by the capillary absorption coefficient, was reduced by over 80 %. Numerical simulations further showed that relative humidity and moisture content at the exterior and middle positions of earthen walls strongly decreased after hydrophobization treatment. The largest moisture flux discrepancy between untreated and treated walls was 652.1 g/(h·m2). Furthermore, the parametric analysis indicated that façade treatment dominated the hygric state of the exterior and middle positions of earthen walls, while ventilation was most important at the wall interior and in the indoor space. Therefore, combining façade hydrophobization treatment and ventilation is recommended to improve the performance of earthen walls and maintain a favorable indoor environment.

A critique on “Predicting capillary absorption of porous stones by a procedure based on an intermingled fractal units model”

In September 2014, this journal published “Predicting capillary absorption of porous stones by a procedure based on an intermingled fractal units model”, which describes the pore volume distribution of building stones via an intermingled fractal units approach and then calculates the capillary absorption coefficient of these materials based on a bundle-of-tubes model. Its results bring about the conclusion that “the sorptivity of natural stones used in historical buildings can be calculated from the pore size distribution determined by MIP”. This critique firstly verifies that there is no need for the detour via the intermingled fractal units, as the bundle-of-tubes approach can be applied on the mercury intrusion results directly. This direct model does though not yield the same capillary absorption coefficients, which resultantly invalidates the agreement between the measured and calculated capillary absorption coefficients reported in the disputed paper. This critique secondly identifies various defects in the disputed paper's calculation of the capillary absorption coefficients, but these do regrettably not readily explain all deviations. These observations bring about serious concerns on the outcomes of the disputed paper, and this critique invites its authors to placate these concerns in their reply.

Utilizing heat-mechanical synergistic treatment for separating concrete waste into high-quality recycled aggregate, active recycled powder and new concrete

Previous literatures highlighted that it is sustainable to reutilize concrete waste as recycled building materials, but a high value-added recycling approach is urgently needed. Therefore, this work investigated the feasibility of using heat-mechanical synergistic treatment at 600–800 °C for separating concrete waste into high-quality recycled aggregate (HRA) and active recycled powder (ARP). The HRA had much lower adhered mortar content and water absorption than ordinary recycled aggregate (ORA); the ARP contained active calcium silicate and calcium oxide, and 800 °C-separated ARP had greater reactivity than 600 °C-separated ARP. Incorporating HRA and intermixing ARP both decreased the compressive strength. However, the HRA blended concrete had greater compressive strength than ORA blended concrete, and the compressive strength of concrete with 100% 800 °C-separated HRA was 14.6% larger than that of concrete with 100% ORA; besides, the concrete with 800 °C-separated ARP had higher compressive strength than the concrete with 600 °C-separated ARP. Although the addition of HRA or ARP raised the transport properties of concrete, HRA blended concrete had lower transport properties than ORA blended concrete, and the concrete with 800 °C-separated ARP had lower transport properties than concrete with 600 °C-separated ARP. At 100% replacement ratio, the capillary absorption coefficient and chloride migration coefficient of concrete with 800 °C-separated HRA were 11.1% and 22.6% lower than those of concrete with 100% ORA. Higher heat temperature can induce extra damage in HRA but elevate the ARP reactivity, and the heat-mechanical synergistic treatment can be adjusted for optimization according to the actual requirement.

Improvement on freeze-thaw durability of municipal solid waste incineration fly ash-based autoclaved wall blocks by triethoxy(octyl)silane/nano-Al2O3 and triethoxy(octyl)silane/graphene nanoplatelets coatings

The envelope structures hardly have the service life up to the design life in severe cold area. Polymer/nano-materials composite coatings are used to enhance the freeze-thaw durability of wall materials. Municipal solid waste incineration fly ash and fly ash were used to fabricate solid wastes-based autoclaved wall blocks (SW-AWBs) with hydrothermal synthesis method. Nano-Al2O3 and graphene nanoplatelets were modified by the coupling agent and used to prepare composite coatings with triethoxy(octyl)silane. Effect of different coatings on the durability of SW-AWBs was compared and discussed. The results showed that the specimens surface changed from hydrophilic to hydrophobic after treated by composite coatings. Meanwhile, the capillary absorption coefficient of SW-AWBs decreased by 57.3%–78.8% and 92.4%–94.1% after treated by triethoxy(octyl)silane/nano-Al2O3 and triethoxy(octyl)silane/graphene nanoplatelets coatings, respectively. Under 15 freeze-thaw cycles, the mass loss of SW-AWBs dropped by 61.9% and 69.4%, the strength loss reduced by 70.5% and 79.4% after treated by triethoxy(octyl)silane/nano-Al2O3 and triethoxy(octyl)silane/graphene nanoplatelets coatings, respectively. Overall, triethoxy(octyl)silane/graphene nanoplatelets had a superior effect on improving the freeze-thaw durability of SW-AWBs than triethoxy(octyl)silane/nano-Al2O3.

Capillary absorption into CEBs and 2-layer composite building materials comprising of natural stone and CEBs

Earth-based building materials have been used since antiquity for the construction of various structures. The main drawback of these materials is their vulnerability to direct contact with liquid water, such as rising damp. To protect earthen structures from rising damp, a stone foundation was used, resulting in composite masonry. In the current study, an experimental investigation of the capillary absorption of non-stabilized CEBs produced with soils sourced from different areas of Cyprus, as well as of 2-layer composite building materials comprising of natural stone and CEBs was carried out. The tests on CEBs indicated that the use of water as the wetting liquid led to the disintegration of the specimens and consequently to non-linear response. Thus, a non-reactive liquid was used instead to measure the capillary absorption coefficient of the materials. The test results showed that the capillary absorption coefficient of CEBs varied between 140-260 gr/m2sec1/2. In the case of the composites, capillary absorption with water as the wetting liquid showed perfectly linear response, following the t1/2 law, with no disintegration of the specimens. The results showed that there are two distinct capillary absorption branches with different gradients, in line with the theory of capillary absorption into 2-layer composite materials.

Evaluation of the efflorescence resistance of calcium sulfoaluminate cement mortar: from indoor accelerated testing to outdoor exposure

Efflorescence is an inevitable phenomenon in all cementitious materials, particularly for Portland cement (PC) - based materials. Considering the relations between ion availability and crystallization, the factors influencing efflorescence involve the compositions of binders, pore structure of the hardened matrix, and so on. This study investigated the efflorescence of calcium sulfoaluminate cement (SAC) mortar at 5–40 °C from perspectives of carbonation potential and pore structure, while PC mortar was chosen as a reference. The microstructure of the efflorescence substances, such as phase assemblage and distribution, was systematically unraveled using optical microscope, in-situ Raman spectroscopy, SEM and EDS at multi scale-level. Water absorption test and XCT were employed for the pore structure characterization. Additionally, an outdoor exposure was carried out to compare with the results from the indoor accelerated experiments. Results reveal that a lower temperature has a limited effect on the efflorescence potential. The dominant efflorescence ingredient for SAC and PC mortars cured at 5–40 °C is CaCO3, with varied polymorphs. However, both primary and secondary efflorescence of SAC mortar is much slighter than that of PC mortar. The volume of fine pores (less than 0.1 mm3) in SAC mortar is higher than that of PC, accompanied by higher capillary absorption coefficient and water absorption rate. However, the low carbonation potential of ettringite tends to be more effective in reducing efflorescence risk for SAC mortar in both lab tests and outdoor exposure. The understanding of the relationship between efflorescence and carbonation provides important insights into the inhibition of efflorescence in cementitious materials.

Salt migration and capillary absorption characteristics of cement mortar partially immersed in NaCl solution

Salt crystallization represents a major reason for the damage observed for porous building materials in humid coastal areas. Despite the several theories developed to explain the process, no unanimous opinion has been proposed for the mechanism underlying the damage. A better understanding of the migration, crystallization, and distribution of salts in porous building materials in the presence of water is thus warranted to improve the durability for cultural heritages and new buildings. This paper reports an experimental study of crystal distribution, micromorphology, chloride ion migration, pore structures, and capillary absorption behaviors of cement-mortar specimens (side-coated and side-uncoated) at three different water-cement ratios (0.4, 0.6, and 0.8) after 120-day partial immersion in 5 wt% NaCl solution. Results showed that the different pore characteristics and side-coating treatment of the specimens governed not only capillary absorption, but also salt migration and distribution. The specimens with a large average pore diameter and greater porosity yielded more external salt crystals, while those with a small average pore diameter and dense surfaces demonstrated the reverse. For vertical migration, the Cl− concentration changed slightly with height of the specimens, except for the top segment. For horizontal migration, the Cl− concentrations in the central samples were higher than the edge samples. Of note, the side-coated specimens were associated with reduced external salt crystals and lower Cl− concentration in their edge samples. Compared with the salt-free specimens, both the capillary absorption coefficient (Acap) and capillary moisture content (Wcap) of the salt-contaminated specimens were lower (water-cement ratio = 0.6, −45.72%, −56.39%; water-cement ratio =0.8, −60.8%, −56.34%), illustrating the inhibitory effect of salt crystallization on the hygroscopic properties of the porous materials. Lastly, both the Acap and Wcap of the side-coated specimens were lower than uncoated ones.

Effect of ion chelator on water sorption and transport behavior of unsaturated mortars with high volume fly ash and blast furnace slag

This paper investigated the effect of ion chelator on water dependency of water transport and fixation in mortars with high volume of fly ash (FA) and blast furnace slag (BFS). Ion chelator (CA) as a new type of crystalline admixture could improve self-healing performance of cementitious materials by crack-healing and pore filling. The porosity of mortar was measured by vacuum saturation and pore size distribution of mortar was tested by low-field nuclear magnetic resonance (LF NMR). The water sorption of mortar was evaluated by water vapor adsorption desorption balance. The water transport of mortar with and without crack was tested by capillary water absorption. Based on the experimental results, the water distribution of capillary water absorption in mortar was calculated. Results showed that the pore structure of mortar was improved evidently by CA, and the pores (>1μm) and the total porosity in mortar containing 50 %BFS were significantly reduced. CA had no obvious effect on the water vapor diffusion coefficient of mortar, but has a significant impact on the liquid water diffusion coefficient, especially in pure cement and containing 50 % BFS mortar. The total capillary water absorption and capillary absorption coefficient of mortars were reduced by CA, especially in pure cement and containing 50 % BFS mortar. The addition of CA decreased the water penetration in mortar, the reduction rates of water penetration depth in experimental groups (with CA) at 360 min were 12.4 % (100 %OPC), 6.0 % (30 %FA), 21.3 % (50 %BFS) and 10.8 % (16 %FA 24 %BFS) compared to control group (no CA). After curing for 42d, the normalized water absorption coefficients S” of cracked M100CA and M50BFS50CA were 55.1 % and 72.0 %, respectively. Ion chelator significantly improved internal pore structure and crack healing ability of the mortar containing 50 %BFS, and then delayed the water diffusion.

Hygric properties of porous building materials (VIII): Influence of reduced air pressure

Hygrothermal properties of porous building materials are indispensable for understanding and optimizing the hygrothermal performance of building enclosures and the built environment. In high-altitude areas, the influence of reduced air pressure on hygrothermal properties should be considered and, if needed, proper corrections should be adopted. Currently, the impact of reduced air pressure on thermal properties has been thoroughly investigated while that on hygric properties remains unclear. In this research, hygric properties of three representative porous building materials – calcium silicate, autoclaved aerated concrete and ceramic brick – are measured at three different air pressures, namely 1.00, 0.80 and 0.60 atm. The static gravimetric test, psychrometer test, cup test and capillary absorption test are performed to obtain the sorption isotherm, moisture retention curve, vapor permeability, capillary absorption coefficient and capillary moisture content. Results show that the influences of air pressure on the sorption isotherm, moisture retention curve, capillary absorption coefficient and capillary moisture content are limited, while the vapor permeability increases obviously with the decreasing air pressure. Specifically, the vapor diffusion resistance factor remains stable in the dry cup test, and this can be predicted by Schirmer's law. In the intermediate cup and wet cup tests, where liquid water contributes to the moisture transfer, the impact from air pressure becomes smaller.

Hardened properties of pre-cracked concrete incorporating metakaolin and crushed blast furnace slag as an additional blend material

• Mechanical and durability properties of pre-cracked modified concrete by metakaolin (MK) and granulated blast furnace slag (GBFS) are studied. • Pre-cracking concretes exposed to sulfuric acid reduces the compressive strength by 45% to 50%. • Increasing the degree of concrete cracking reduces the compressive strength and the durability of the concretes after acid exposure. • A positive effect of additives (MK and GBFS) on the durability of the concrete is noted. • Replacement of cement with additives at 10% is the better mix design for concrete. In this research paper, an experimental study was carried out to analyze the durability of pre-cracked modified concrete by metakaolin (MK) and ground granulated blast furnace slag (GBFS). The mechanical and durability properties of three different types of hardened concrete and conventional cement concrete were assessed in terms of compressive strength, mass loss, open porosity, water penetration, capillary water absorption, and drying shrinkage for two compressive damage levels subjected to sulfuric acid attack (concentration of 5%). After the immersion period, these proprieties were compared with those of the control mix, and the variation in different parameters was evaluated. The results show that incorporating MK and GBFS improves the compressive strength in the long term compared to control concrete. In addition, the exposition of pre-cracking concrete to sulfuric acid reduces by 45% to 50% of the compressive strength of the concrete for all formulations. These results are confirmed by the mass loss and the pre-cracking samples’ open porosity variation. The F10 formulation provided the lowest water penetration depth and capillary absorption coefficient compared to the control mix regardless of the degree of cracking and exposure to acid, which shows the positive effect of additives on the durability of the concrete. The replacement of cement with MK and GBFS at 10% is considered the better mix design for concrete of sewer structures. The shrinkage of this mix was the lowest compared to the other formulations.

Efflorescence inhibition and microstructure evolution of Portland cement-based artificial stone induced by mineral additives

Portland cement-based artificial stone is one of the most important construction materials, but the high risk of efflorescence limits its application. Metakaolin, nano-SiO2 and basalt powder were used as mineral additives in Portland cement stone to inhibit efflorescence in this work. The efflorescence of cement stone was investigated from perspectives of hydration products and pore structure. Both morphology and phase assemblage of efflorescence substance was studied through optical microscope, laser confocal Raman spectroscopy and SEM at various scales. Results show that the addition of nano-SiO2 and metakaolin can effectively inhibit the efflorescence of cement stone, due to the consumption of Ca(OH)2 during cement hydration and the decline in total porosity. By contrast, nano-SiO2 with higher reactivity and specific surface area exhibits the best efflorescence resistance, accompanied with the least amount of macro-pores and total porosity, the lowest capillary absorption coefficient and portlandite content.

The Inhibitive Effect of Sebacate-Modified LDH on Concrete Steel Reinforcement Corrosion

In recent decades, layered double hydroxides (LDH) have been proposed as innovative corrosion inhibitors for reinforced concrete. Their protective action is based on the ability to intercalate specific anions in the interlayer and on their ability to exchange the intercalated anion. In the present study, an organically charged LDH, with sebacate anions in the interlayer (LDH-S), is proposed as a water-repellent additive for mortar. The waterproofing efficiency of LDH-S and the associated corrosion inhibition ability has been evaluated in reinforced mortar samples. A 42% decrease in the water capillary absorption coefficient has been estimated when 3% LHD-S is added to a mortar. Both the passivation processes of the steel rebars during the curing period and the initiation of corrosion due to chloride exposure have been studied by electrochemical measurements. Three different mortars have been evaluated: reference mortar (REF), mortar with Mg-Al LDH (LDH), and mortar with LDH-sebacate (LDH-S). The latter has shown an important protective capacity for preventing the initiation of corrosion by chloride penetration, with an inhibitory efficiency of 74%. The presence of LDHs without sebacate in the interlayer also improved the performance of the mortar against rebar corrosion, but with lower efficiency (23% inhibitory efficiency). However, this protection is lost after continued chloride exposure over time, and corrosion initiates similarly to the reference mortar. The low corrosion current density values registered when LDH-S is added to the mortar may be related to the increased electrical resistance recorded in this mortar.