High-performance Cement-based Materials Research Articles

Mechanical performance, impact behavior and environmental assessment of coal furnace slag based low-carbon ultra-high performance engineered cementitious composites (UHP-ECC)

This study aimed to optimize the utilization of industrial solid waste through developing a high-performance cement-based composite material (UHP-ECC), incorporating coal furnace slag (CFS) and waste rubber powder (RP). The investigation concentrated on the effects of introducing 10% RP into UHP-ECC and replacing ordinary Portland cement (OPC) with CFS at varying proportions (0%, 20%, 40%, 60%) on mechanical properties, impact resistance, and sustainability. The mixtures underwent a comprehensive characterization, including mechanical tests, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), to clarify hydration mechanisms and microstructural features. The results revealed that the addition of 10% rubber led to flaws, resulting in a minor reduction in compressive strength from 143.2 MPa to 132.2 MPa. Substituting 20% with CFS resulted in a denser matrix, raising the compressive strength to 135.5 MPa. CFS decreased the initial cracking strength and matrix fracture toughness, with tensile strain peaking at 8.05% and narrower crack widths. More CFS content yielded a slight decrease in peak impact force but induced more fine cracks and enhancing ductility. Moreover, as CFS is a waste product generated at high temperatures, the mixture demonstrated outstanding impact performance at 150 °C, absorbing rather than converting more energy into kinetic energy. Comparative analysis against similar mixtures highlighted UHP-ECC's strengths in embodied carbon, embodied energy, and material cost. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) assessment identified the CFS40-R10 as better mixture, achieving a balance between mechanical performance, cost-effectiveness, and sustainability. Microscopic analysis revealed that up to 40% CFS facilitated hydration, and the 60% CFS mixture exhibited the lowest total mass loss at high temperatures.

Residual impact resistance behavior of PVA fiber reinforced cement mortar containing Nano-SiO2 after exposure to chloride erosion

High-performance cement-based composite materials are commonly employed in marine structural engineering. However, the deterioration of mechanical and durability properties of composite structures caused by chloride erosion in marine environments is a typical engineering problem. This study aims to assess the impact of NS and PVA fibers on the strength, chloride resistance, and impact resistance of NS-PVA fiber mortar. The impact frequency distribution of NS-PVA fiber mortar was analyzed under two conditions: natural environment and after chloride erosion, utilizing both log-normal and two-parameter Weibull distribution models. The findings indicate that the impact energy consumption of NS-PVA fiber mortar increases after 28 days of chloride erosion compared to the natural environment, primarily due to the formation of a compact pore structure attributed to the reaction product Friedel's salt. The optimal composite dosage is determined to be 1.8% for NS and 1 vol% for PVA fiber. At this dosage, the PS18 mortar exhibits a 44.8% and 53.7% increase in initial cracking and failure impact energy, respectively, compared to conventional mortar in the natural environment. Furthermore, these enhancements are further amplified to 53.4% and 64.6% after chloride erosion. Concurrently, a negative correlation is observed between accelerated impact energy consumption and chloride diffusion depth in NS-PVA fiber mortar. A predictive model for impact energy consumption of NS-PVA fiber mortar following chloride erosion, considering various failure probabilities, is established, offering valuable insights for the practical application of NS-PVA fiber mortar in marine engineering.

Effect of Chemical Admixtures on the Working Performance and Mechanical Properties of Cement-Based Self-Leveling Mortar

In this work, the effect of cellulose ether (CE), tartaric acid (TA), and polycarboxylate superplasticizer (PCE) on the working performance and mechanical properties of cement-based self-leveling mortar is investigated. According to the orthogonal experiment analysis, TA is identified as the most influential factor affecting the working performance, as indicated by factors such as fluidity, fluidity loss, and viscosity. Upon conducting a comprehensive assessment of the working performance and mechanical properties, the optimal parameters are found to be CE = 0.6 wt.‰, TA = 0.5 wt.‰, and PCE = 2.0 wt.‰. A univariate test highlights that that the working performance improves with the higher TA dosages. Specifically, the exponential reduction of fluidity loss corresponds with an increased TA content. Regarding the mechanical properties of cement-based self-leveling mortar, the compressive and flexural strength exhibit enhancement when the TA dosage remains below 0.4 wt.‰ at the early stage, implying that TA has some influence on the hydration process. Impressively, the 1 d compressive and flexural strengths surpass 7 MPa and 2 MPa, respectively, ensuring the viability of subsequent construction activities. Through an analysis of hydration heat, the effect mechanism of TA on the cement-based self-leveling mortar is derived. The result shows that the addition of TA decelerates the hydration process within the initial 10 h, followed by acceleration in the subsequent 20 h to 30 h. Consequently, this delayed formation of the early hydration product, ettringite, contributes to a more porous structure in the slurry, with low friction leading to a better working performance. A large number of hydration products, such as alumina gel and calcium–silicon–hydrate gel, presented in the hardened paste results in the good mechanical properties at 1 d. This study may lay a foundation for the optimization of the dosage of chemical admixtures in the self-leveling mortar and high-performance cement-based materials, and also impart valuable insights for practical applications extending to the realm of building construction and decoration.

Seismic behavior of shear walls partially strengthened with UHPC in boundary element

Inspired by studies on shear walls reinforced with high performance cement-based materials, this paper explores the applicability of ultra-high performance concrete (UHPC) for improving the seismic behavior of shear walls. In this study, a novel shear wall partially strengthened with UHPC in the boundary element was developed, in which the UHPC was cast into the potential plastic hinge region of the boundary element. Partial application of UHPC can reduce construction costs and promote its use in building structures. To study the influence of distribution height and width of UHPC and axial load ratio on the seismic performance, six shear walls with a shear span ratio of 2.1 were tested under axial load and cyclic lateral load. The failure modes, lateral load-lateral displacement hysteretic behavior and ductility of the shear walls were also investigated. The experimental results indicated that the partial application of UHPC in boundary elements could effectively improve the performance of shear walls. Moreover, even if the volume ratio of UHPC was only 0.12, the shear wall partially strengthened with UHPC still showed good seismic performance under a high axial load ratio, indicating that this type of shear wall can be applied to the high seismic intensity and high axial load ratio regions.

Performance and microscopic study of various mineral admixtures on reactive powder concrete

A ternary admixture system of industrial waste (silica fume (SF), slag powder (SL), and fly ash (FA)) was used to replace quartz powder and reduce the cement content to prepare green, low-carbon and high-performance cement-based materials. The mechanical properties of RPC under natural watering curing (NWC), standard curing (TC), and mixed curing (MC) conditions were studied, and the influencing mechanism was analyzed and explored from a microscopic perspective. The results show that the MC curing system promotes the early hydration of cement and improves the compactness of the matrix. However, the strength in the later stage was affected by temperature internal force, and the compressive and splitting tensile strength in the later stage increased by −0.1% and −36.27%, respectively. The 28 day compressive strength of RPC under TC and NSC conditions increased by 10.30% and 11.78% compared to 7 days, while the splitting tensile strength increased by 17.42% and 14.10%, and the difference between RPC and MC strength gradually decreased.

Characterizing the bending behavior of underground utility tunnel roofs in a fabricated composite shell system

The traditional underground utility tunnel system is characterized by a lengthy construction period, material waste, and poor engineering quality. This study proposes the prefabricated composite shell system underground utility tunnel as a new type of prefabricated underground utility tunnel system. This system uses 20 mm thick high-performance cement-based materials as permanent templates, with steel reinforcement skeletons placed in the cavity between the two side molds, and concrete can be poured after on-site hoisting and positioning to form an integrated tunnel. This study first systematically introduces the system design method of the prefabricated composite shell system underground utility tunnel and clarifies its component and connection structures. Then, bending tests are conducted on the composite shell tunnel top plate specimens, and a cast-in-place top plate specimen is selected as a control group. A suitable bearing capacity calculation formula for composite shell top plates is derived and proposed based on test phenomena and results analysis. The results showed that the prefabricated outer template and internal cast-in-place concrete of the composite shell top plate specimen have good collaborative performance. Its bearing capacity, stiffness, and failure phenomena are consistent with those of cast-in-place components, as are its mechanical properties. In addition, the proposed bearing capacity calculation formula for a composite shell top plates is highly accurate and can guide the design of such components.

Effect of Biochar Dosage and Fineness on the Mechanical Properties and Durability of Concrete

Biochar (BC), a byproduct of agricultural waste pyrolysis, shows potential as a sustainable substitute material for ordinary silicate cement (OPC) in concrete production, providing opportunities for environmental sustainability and resource conservation in the construction industry. However, the optimal biochar dosage and fineness for enhancing concrete performance are still unclear. This study investigated the impact of these two factors on the mechanical and durability properties of biochar concrete. Compressive and flexural strength, carbonation resistance, and chloride ion penetration resistance were evaluated by varying biochar dosages (0%, 1%, 3%, 5%, 10%) and fineness dimensions (44.70, 73.28, 750, 1020 μm), with the 0% dosage serving as the control group (CK). The results showed that the addition of 1-3 wt% of biochar could effectively reduce the rapid carbonation depth and chloride diffusion coefficient of concrete. The compressive and flexural strength of BC concrete initially increased and then decreased with the increase in biocarbon content, BC with a fineness of 73.28 μm having the most significant effect on the mechanical strength of concrete. At the dosage of 3 wt%, BC was found to promote the hydration degree of cement, improving the formation of cement hydration products. These findings provide valuable insights for the development of sustainable and high-performance cement-based materials with the appropriate use of biochar as an additive.

Učinak recikliranog stakla kao agregata na svojstva mikrobetona

Micro-concrete (MC) can be defined as a high-performance cement-based material produced using microaggregates and cement in the required proportions. Owing to its high performance, it has the potential to be used in the structural repairs of existing building elements. Within the scope of this study, an evaluation was conducted by creating a usage scenario under which glass, which is a waste product, can be reduced and applied in a way that provides a sufficient MC performance. There are four different binder contents in the mixtures within the scope of the present study, i.e., 570, 580, 599, and 658 kg/m3. From these mixtures, together with the control mixture, 12 %, 27 %, and 50 % microaggregates were replaced with glass sand and 16 different mixtures with a total of 4 different aggregate contents were produced. For the mechanical, physical, and durability tests, 40 × 40 × 160 mm sized prisms and 50 × 50 × 50 mm sized cubes were produced. For the purposes of this research, mechanical tests were carried out on 144 7-, 28- and 56-day old prismatic specimens. In addition, the effects of a freeze-thaw and temperature on the mechanical properties were investigated on 192 prismatic samples. In determination of the durability, physical properties such as the porosity, sorptivity, and specific gravity were tested and determined using cubic samples. The test results show that the replacement of MA with GS has positive effects on all mechanical behaviours of MC.

Carbon nanotubes assisted fly ash for cement reduction on the premise of ensuring the stability of the grouting materials

Cement-based grouting is the most used method to strengthen the fractured rock mass and reinforce the mechanical properties and impermeability of the surrounding rock. The balance among the strength, durability, workability and cost of the grout has always been the key to grouting engineering. In this study, we use carbon nanotubes (CNTs) as the nano-additive to assist fly ash in preparing high-performance cement-based grouting materials. The results show that CNTs can generate nucleation effects and pore-filling effects in cementitious composites to promote the hydration reaction of the grouting materials and optimize the pore structure of the hardened slurry. Two reinforcing roles, bridging and pulled-out role of CNTs, act in the hardened cement matrix, where the former can improve the mechanical properties of grouting materials through micro-friction toughening, and the latter can form a net-like distribution in cement matrix together to enhance the impermeability. More importantly, we found that 0.08 wt% CNTs combined with 20 wt% fly ash can be a good substitute for cement with a moderate proportion of grouting materials. Compared with plain cement slurry, the mechanical properties are basically unchanged, while the workability can be increased by about 5%, and the impermeability can be reinforced by 6%. The discovery of this research provides an excellent chance for utilizing the superior properties of CNTs to fabricate high-performance, cost-effective and environment-friendly grouting materials.

Multi-scale synergistic modification and mechanical properties of cement-based composites based on in-situ polymerization

For the multi-scale and multiphase composite structure, modifying cement-based material at different scales to improve structural and mechanical performance is necessary. This paper developed a continuous multi-scale synergistic modified cement-based material with excellent properties by polymers, whiskers, and fibers. Notably, the polymer network is formed by in-situ polymerization in the hydration process of cement and works in concert with different scales modified substances. Specifically, the effect of in-situ polymerization of acrylamide monomers (IPAM), calcium carbonate whiskers (CW), and polyvinyl alcohol (PVA) fibers on mechanical strength is analyzed by response surface methodology, and the optimal mix ratio design is obtained. With the optimized mix ratio, the flexural strength of multi-scale modification samples is increased by more than 135% compared to the neat paste, while the 28d compressive strength is maintained essentially the same, with only a 2.9% reduction. And multi-scale samples' properties are significantly improved compared to single-scale samples. In addition, multi-scale composites' mechanical properties and microstructure are characterized in detail to investigate the incredible performance and the modification mechanism. Three modified materials form a continuous micro-meso-macro multi-scale structure in the cement matrix. Moreover, the interaction between IPAM, CW, and PVA fibers is confirmed. The IPAM can in-situ modify the interfacial structure of fibers and whiskers, strengthen the interrelation between different scales, resulting in exciting enhancements of the cement-based composite's structure and performance. This multi-scale modification strategy provides new ideas and promising applications for preparing high-performance cement-based materials.

Floating breakwater pontoon pilot cast with carbon textile reinforcement-based ultra high durability concrete: Materials development and testing, and implementation in the North Atlantic (Irelands west coast)

A floating unit with three pontoons made of epoxy-coated carbon textile reinforced, ultra-high durability concrete (ECF UHDC), mineral impregnated carbon fibre-reinforced UHDC (MCF UHDC) and, as references, steel-reinforced concretes has been designed and installed in the Northern Atlantic. While marine structures with steel reinforcement require large cover depths, which cause problems in size, cost, environmental friendliness and short service life, carbon textile reinforced concrete (TRC) cannot suffer from chloride-induced corrosion of a metal reinforcement. In the EU H2020 project “ReSHEALience” (rethinking coastal defence and green-energy service infrastructures through enhanced-durability highperformance cement-based materials), TRCs have been modified with functional admixtures from consortium partners. A mineral self-healing promoter and alumina nano-fibers have, among others, been implemented to boost high-performance concretes towards UHDCs. Resulting composite variants have been applied in a full-scale floating unit that has been launched in the harbor of Galway at the Irish West Coast in June 2020. Such a floating body is a representation of breakwaters installed to reduce wave impacts to the coast. Besides, TRC-based UHDC can be applied as strengthening and repair layer on concrete structures to enhance their service life in general.

Self-healing of high-performance engineered cementitious materials with crystalline admixture in the seawater environment

The present paper studies the crack healing effect of high-performance cement-based materials mixed with crystalline admixture (CA) in seawater environments. Specifically, the healing effects of specimens with different initial crack widths in tap water and seawater environments were investigated through the seepage healing test (simulating a structure that a side contact with water and the other side contact with air). The variations of seepage velocity and water flow in the early 24 h of healing were mainly investigated. It was found that crystalline materials delay the healing of cracks in the initial stage of healing and this defect is more obvious under the seawater healing condition. Inductive Coupled Plasma (ICP) test was used to detect the variation of ion concentration in seawater; XRD, FTIR, and TG tests were carried out for characterizing the composition and relative content of healing products in the crack under the seawater and tap water healing conditions. Moreover, the effect of CA on the composition of healing products and the effect of crack width on healing products were quantified. The distribution characteristics of healing products along the crack depth under seawater seepage and seawater immersion healing conditions were then obtained.

Assessing the Structural Behavior of a New UHPC-Infilled Top Chords Integrated Deck Plate System at Construction Stage

In this paper, a new deck plate system, in which the top chords are infilled with high-performance cement-based material such as high-strength mortar and UHPC (ultra-high performance concrete), was proposed. The bending capacity of the proposed deck plate system at the construction stage was investigated by performing a four-point bending test on seven specimens with a net span of 4.6 m. Test parameters included the type of top chords, type and amount of infilled material, and existence of inner shear connectors. The load versus displacement curves were plotted for all the specimens, and their failure modes were identified. In addition, a theoretical strength estimation process was developed for the proposed deck plate system. The strength values calculated by the estimation process were compared with the test results and analyzed. This comparison showed that the proposed system retained the peak strength and initial stiffness at a much higher level than the conventional system, and the theoretical strength estimation process can predict the failure modes and peak strength of the proposed system accurately.

Research on the Hydration and Mechanical Properties of NAC-Hardened Cement under Various Activation Methods

Adding mineral admixture is one of the leading technical ways to improve the durability of cement-based materials. Nano attapulgite clay (NAC) is a unique fiber rod crystal structure that can change the physical and mechanical properties of cement-based materials, and opens up a new idea for exploring the durability of high-performance cement-based materials. This paper studied the effects of NAC on the hydration process, pore structure, and mechanical properties of a cement substrate under different activation methods. The results show that the pH value of the pore solution of cement mixed with 5% NAC high-viscosity ore (calcined) was 8.8% higher than that of the cement without NAC. The chemically bound water contents in the 1% and 3% NAC raw (calcined) cement were 14.11% and 14.04%; when the content of calcined NAC raw ore was 1%, the improvement effect on the cement hydration process is the best. The content of calcined NAC was 1%, 3%, and 5%, and the porosity of hardened cement paste was 19%, 19.04%, and 22.27% lower than that of the cement without NAC. Calcining NAC raw ore can improve cement’s hydration process, promote cement’s hydration reaction, and increase the compactness of hardened cement paste. The fluidity of the cement mortar mixed with calcined high-viscosity ore (D and E) at a mixing amount of 5% was reduced by 32.66% and 26.13%, respectively, compared to the ordinary specimens. The flexural strength of the cement paste mixed with calcined raw ore and high-viscosity ore at a mixing amount of 1% was generally improved by 28.40% and 17.28% compared to the cement without NAC paste. After calcination, the NAC raw ore is better than the high-clay ore in improving the mechanical properties of cement.

Numerical and theoretical analysis of beam-to-column connections with ECC ring beams subjected to local compression loading

Engineered cementitious composite (ECC) is a kind of high performance cement-based composite materials with strain hardening and multiple cracking behaviour. Replacing concrete with ECC in the beam-to-column connection with ring beam may effectively improve the load-carrying capacity and ductility, as well as prevent cracks and solve durability problems caused by the brittleness of concrete. In this paper, the failure mechanism of beam-to-column connection with ECC ring beam subjected to local compression loading was investigated with the nonlinear finite element (FE) method. The results indicated that continuous lateral pressure was provided by the ECC ring beam, which improved the local compression performance of the ring beam connection. Extensive parametric studies on the local compression behavior of connections with ECC ring beams were also conducted. According to the simulation results, the peak strength of ECC connections was 13.0%–24.2% higher than that of concrete specimens. Increasing the ECC compression strength or ring beam width can effectively increase the load-carrying capacity of the connection, but the ECC tensile strain can only affect the ductility of the connection when the ultimate tensile strain was lower than 1.5%. Based on the FE analysis, an effective restraint width of the ECC ring beam was proposed, and theoretical models were established to predict the axial compressive bearing capacity of the beam-to-column connection with ECC ring beam.

Development of Green Cementitious Materials by Using the Abrasive Waterjet Garnet Wastes: Preliminary Studies

The constant need for recycling, waste prevention and general environmental protection represent the new directive approaches imposed by the geo-political, industrial and environmental context, at the regional, European and global level. Ensuring the environmental protection and reducing the natural resources consumption represent general purposes of the sustainable development and also considerations to implement the Circular Economy Model [1]. The present study is developed with respect to the previously mentioned principles: the waterjet cutting operations by the use of abrasive GARNETs for quality, speed and accuracy gain, are in continuous expansion, generating proportionally increasing wastes, which could be valorized by innovatively integrating them in advanced cementitious materials for the construction industry. The international research regarding the use of abrasive waterjet Garnet wastes as raw material for construction industry are at incipient stage and quite limited, but preliminary results are promising. Further studies are presently developed, considering the potential benefits and also the reduced toxicity degree of abrasive Garnet wastes. This paper offers a general overview concerning the recent studies performed in the topic of efficient use of abrasive Garnet wastes in different building materials. Supplementary, further research, both theoretical and experimental is considered, for developing green, advanced, high performance cement-based materials by using the abrasive waterjet Garnet wastes, mainly as fine grain addition or replacement in the composites.

Exploration Testing on High-Performance Cement-Based Materials Using Granulated Blast Furnace Slag as Fine Aggregates

This study investigates the feasibility of using granulated blast furnace slag (GBFS) as fine aggregates for high-performance cement-based (HPCB) materials. The mixture ratio of HPCB materials using GBFS as fine aggregates is calculated based on the dense packing theory of aggregates and the minimum water requirement. A series of cement-based material mixes are prepared with three water binder ratios (0.16, 0.18, and 0.2) and three GBFS replacement ratios (0%, 50%, and 100%). Various properties of the cement-based materials, such as the compressive strength, flexural strength, splitting tensile strength, and elastic modulus, are studied. The research on the selected HPCB material compositions using scanning electronic microscopy (SEM), hardened concrete pore structure determination (HCPD), and mercury intrusion porosimetry (MIP) enables a further understanding of the relationship between the mechanical properties and microstructures. The test results show that it is feasible to produce HPCB materials using GBFS as fine aggregates. Despite its large crushing value index and irregular particle shape, GBFS has hydraulic properties that can make up for these disadvantages. GBFS and mixed fine aggregate cement-based materials with good properties can be prepared with a reasonable mix design. The strength of such cement-based materials is consistent with that of ordinary quartz sand (QS) fine aggregate cement-based materials. The compressive, flexural, and splitting tensile strengths of GBFS and mixed fine aggregate cement-based materials may be higher than those of ordinary QS fine aggregate HPCB materials. The relationship between the compressive strength and porosity is in agreement with the formulas proposed by Powers, Ryshkevitch, Schiller, and Hasselman.

Durability-Based Design of Structures Made with Ultra-High-Performance/Ultra-High-Durability Concrete in Extremely Aggressive Scenarios: Application to a Geothermal Water Basin Case Study

This paper provides the formulation and description of the framework and methodology for a Durability Assessment-based Design approach for structures made of the Ultra-High-Durability Concrete materials conceived, produced and investigated in the project ReSHEALience (Rethinking coastal defence and Green-energy Service infrastructures through enHancEd-durAbiLity high-performance cement-based materials) funded by the European Commission within the Horizon 2020 Research and Innovation programme (Call NMBP 2016–2017 topic 06-2017 GA 780624). The project consortium, coordinated by Politecnico di Milano, gathers 13 partners from 7 countries, including 6 academic institutions and 7 industrial partners, covering the whole value chain of the concrete construction industry. The innovative design concept informing the whole approach herein presented has been formulated shifting from a set of prescriptions, mainly referring to material composition and also including, in case, an allowable level of damage defined and quantified in order not to compromise the intended level of “passive” protection of sensitive material and structural parts (deemed-to-satisfy approach; avoidance-of-deterioration approach), to the prediction of the evolution of the serviceability and ultimate limit state performance indicators, as relevant to the application, as a function of scenario-based aging and degradation mechanisms. The new material and design concepts developed in the project are being validated through design, construction and long-term monitoring in six full-scale proofs-of concept, selected as representative of cutting edge economy sectors, such as green energy, Blue Growth and conservation of R/C heritage. As a case study example, in this paper, the approach is applied to a basin for collecting water from a geothermal power plant which has been built using tailored Ultra-High-Durability Concrete (UHDC) mixtures and implementing an innovative precast slab-and-buttress structural concept in order to significantly reduce the thickness of the basin walls. The geothermal water contains a high amount of sulphates and chlorides, hence acting both as static load and chemical aggressive. The main focus of the analysis, and the main novelty of the proposed approach is the prediction of the long-term performance of UHDC structures, combining classical structural design methodologies, including, e.g., cross-section and yield line design approaches, with material degradation laws calibrated through tailored tests. This will allow us to anticipate the evolution of the structural performance, as a function of exposure time to the aggressive environment, which will be validated against continuous monitoring, and pave the way towards a holistic design approach. This moves from the material to the structural durability level, anticipating the evolution of the structural performance and quantifying the remarkable resulting increase in the service life of structures made of UHDC, as compared to companion analogous ones made with ordinary reinforced concrete solutions.

Using Graphene Sulfonate Nanosheets to Improve the Properties of Siliceous Sacrificial Materials: An Experimental and Molecular Dynamics Study.

The fabrication of high-performance cement-based materials has benefited greatly from the extensive use of graphene and its derivatives. This paper studies the effects of graphene sulfonate nanosheets (GSNSs) on sacrificial cement paste and mortar (the tested materials) and other siliceous sacrificial materials, especially their ablation behaviors and mechanical properties. Decomposition temperatures and differential scanning calorimetry were used to examine how different contents of GSNSs determines the corresponding decomposition enthalpy of the tested materials and their ablation behaviors. Molecular dynamics was also used to clarify the mechanism how the GSNSs work in the CSH (calcium silicate hydrated)/GSNSs composite to increase the resistance to high temperature. The experimental results show that: (1) the contents of GSNSs at 0.03 wt.%, 0.1 wt.%, and 0.3 wt.% brought an increase of 10.97%, 22.21%, and 17.56%, respectively, in the flexural strength of siliceous sacrificial mortar, and an increase of 1.92%, 9.16%, and 6.70% in its compressive strength; (2) the porosity of siliceous sacrificial mortar was decreased by 5.04%, 9.91%, and 7.13%, respectively, and the threshold pore diameter of siliceous sacrificial mortar was decreased by 13.06%, 35.39%, and 24.02%, when the contents of GSNSs were 0.03 wt.%, 0.1 wt.%, and 0.3 wt.%, respectively; (3) a decline of 11.16%, 28.50%, and 61.01% was found in the ablation velocity of siliceous sacrificial mortar, when the contents of GSNSs were 0.03 wt.%, 0.1 wt.%, and 0.3 wt.%, respectively; (4) when considering the ablation velocities and mechanical properties of siliceous sacrificial materials, 0.1 wt.% GSNSs was considered to be the optimal amount; (5) the GSNSs contribute to the reinforced effect of GSNSs on CSH gel through the grab of dissociated calcium and water molecules, and the chemical reaction with silicate tetrahedron to produce S–O–Si bonds. These results are expected to promoting the development of new kinds of siliceous sacrificial materials that contain GSNSs.

Novel microcapsules for internal curing of high-performance cementitious system

Conventional internal curing materials for high-performance cementitious system cannot easily have artificial modifications, such that the curing effect is difficult to control during the process. In this study, a novel microcapsule is proposed for controlled internal curing of cement-based materials. The microcapsules are synthesized by a double emulsion method to form a polymer shell-water core structure. The sensitivity of polymer shell to alkaline environments is used to trigger the release of core water. Thus, water release can be controlled by tailoring the shell thickness and microcapsules sizes by changing the polymer dosage and stirring rate during synthesis. The experimental results indicate that the novel microcapsules can effectively release water for internal curing of a cementitious matrix, which exhibits a high curing efficiency in terms of nearly autogenous shrinkage and increases the compressive strength. The novel microcapsules could be promising internal curing agents to enhance high-performance cement-based materials.