Porous Cement Research Articles

A two-step homogenization micromechanical model for strain-sensing of graphene reinforced porous cement composites

The incorporation of graphene and its derivatives into cement for electrically conductive composites is currently under extensive investigations due to their potential applications as smart materials for large-scale self-sensing structures. It is of great importance to develop theoretical models to predict the response of the electrical conductivity of the cement composites when subjected to mechanical deformation. Experimental studies have demonstrated that pores and rippled graphene fillers exist in the cement composites. However, currently there are limited theoretical models to predict the electrical conductivity and piezoresistive properties of the cement composites with incorporating the effects of pores and graphene ripples. To address the research gap, this paper develops a two-step micromechanical modelling to predict the effective electrical conductivity and the response of conductivity to compression strain of graphene nanoplatelet (GNP) reinforced cement composites (GNPRCCs) with considering the effects of pores and graphene ripple for the first time. The effective medium theory and Mori-Tanaka model are employed to homogenize the GNP and pores as inclusions with considering several influencing mechanisms. Parametric study is carried out to identify the effects of the attributes of GNPs, pores and electron tunnelling on the electrical and piezoresistive properties of the GNPRCCs. It is found that the piezoresistive response is proportional to porosity when the conductive behavior of GNPRCC is dominated by the tunnelling effect. Increasing porosity has a negative impact on the strain-sensing performance of the GNPRCCs once the conductive network is formed.

Porous silicate cement membranes generated by the novel method combining freeze casting and heat-dry curing

Porous silicate cement membranes (PSCMs) fabricated by the freeze casting method show great potential to be utilized in seawater pretreatment, fermentation broth separation, and industrial wastewater treatment due to its merit of high-temperature resistance, low-cost, and hierarchically ordered porous structures, while the freeze casting method is complex and time-consuming. In this work, a combination of freeze casting and heat-dry curing was initially applied to generate PSCMs. The preparation periods of PSCMs could be shortened by simplifying preparation processes and reducing curing time. The resulting membranes presented double-layer structures, containing a nucleation zone (N-zone) with dense structures and a stability zone (S-zone) with lamellar pore structures. The X-ray diffraction pattern of membranes displayed the mixed hexagonal and rhombohedral structures. This novel method could save more than half of energy consumption compared with the traditional preparation technology of silicate cement samples. The membranes with a mesopore size of 3.794 nm showed high permeation performance with pure water flux reaching 207.23 L m−2 h−1 under 0.15 MPa and room temperature. The separation efficiency of oil-water was 78.05% under operating pressure of 0.05 MPa. Molecular dynamics simulation was applied to narrate the microscopic process of transformation during heat-dry curing, and obtained a good similarity of consequences between the computational method simulation and experimental operation.

Porous polymer cement composites for quasi-solid graphene supercapacitors

We reported a strong and cheap polymer modified Portland cement (PC) composites with interconnected pores as solid electrolyte for graphene supercapacitors. The porous polymer cement composites solved the low ionic conductivity question of construction materials. Herein, the effects of PAA molecular weight, PAA content and curing age on electrical energy storage and mechanical property were investigated in detail. The PAA (Mw = 5000)/PC-5 % sample delivers the best multifunctionality. Moreover, the as-assembled solid supercapacitor exhibits an optimum energy density of 15.93 mW h cm−2, as well as a considerable compressive strength of 16.2 MPa at 28 days. In addition, introducing PAA can result in high porosity which is conductive to ion migration. The symmetric electrode is directly loaded with GO on Ni foam by electrophoretic, followed by high temperature thermal reduction. The integrated solid supercapacitors are effective, holistic and effortless to operate at room temperature, and they exert a crucial role in energy storage field of inorganic building materials application.

The green paving block made from the broken lightweight concrete brick: the preliminary study

Presently, construction the building walls with lightweight concrete blocks in Thailand is very popular; however, lightweight concrete blocks are easily damaged during transportation to the construction sites. The waste generated from damaged lightweight concrete blocks requires proper management with an additional budget. Reusing the broken lightweight concrete block as aggregate for the concrete paving block is one of the waste management alternatives. Therefore, this research aims to evaluate the characteristics of concrete paving block made by broken lightweight blocks. The tests required by the Thai Industrial Standards Institute were followed in the research. The replacement percentages of the broken block by mixture weight equivalent to 0%,10%,20%, and 30% were employed to reduce the virgin-coarse aggregate used for concrete paving block manufacturing. The test results revealed that the compressive strength of the concrete paving block reduced by 0.06 ksc at every 1% of replacing the virgin aggregate by broken lightweight block. Moreover, the water absorption of the concrete paving block increased with the rise in amount of broken lightweight blocks. These might be caused by the porous cement mortar adhered on the broken lightweight blocks. Therefore, the modification of broken lightweight blocks is required prior to employ this waste as the aggregate for concrete paving block mixture.

Bioorthogonal "Click Chemistry" Bone Cement with Bioinspired Natural Mimicking Microstructures for Bone Repair.

Current bone cement systems often demand free radical or metal-related initiators and/or catalysts for the crosslinking process, which may cause serious toxicity to the human body. In addition, the resultant dense scaffolds may have a prolonged degradation time and are difficult for cells to infiltrate and form new tissue. In this study, we developed a porous "click" organic-inorganic nanohybrid (PO-click-ON) cement that crosslinks via metal-free biorthogonal click chemistry and forms porous structures mimicking the native bone tissue via particulate leaching. Strain-promoted click reaction enables fast and efficient crosslinking of polymer chains with the exclusion of any toxic initiator or catalyst. The resulting PO-click-ON implants supported exceptional in vitro stem cell adhesion and osteogenic differentiation with a large portion of stem cells infiltrated deep into the scaffolds. In vivo study using a rat cranial defect model demonstrated that the PO-click-ON system achieved outstanding cell adsorption, neovascularization, and bone formation. The porous click cement developed in this study serves as a promising platform with multifunctionality for bone and other tissue engineering applications.

Speciation of iron(II/III) at the iron-cement interface: a review

Steel is used as reinforcement in construction materials and it is also an important component of cement-stabilized waste materials to be disposed of in deep geological repositories for radioactive waste. Steel corrosion releases dissolved Fe(II/III) species that can form corrosion products on the steel surface or interact with cementitious materials at the iron-cement interface. The thermodynamically stable Fe species in the given conditions may diffuse further into the adjacent, porous cement matrix and react with individual cement phases. Thus, the retention of Fe(II/III) by the hydrate assemblage of cement paste is an important process affecting the diffusive transport of the aqueous species into the cementitious materials. The diffusion of aqueous Fe(II/III) species from the steel surface into the adjacent cementitious material coupled with the kinetically controlled formation of iron corrosion products, such as by Fe(II) oxidation, decisively determines the extension of the corrosion front. This review summarises the state-of-the art knowledge on the interaction of ferrous and ferric iron with cement phases based on a literature survey and provides new insights and proper perspectives for future study on interaction systems of iron and cement.

The Preparation of Photocatalytic Porous Magnesium Oxychloride Cement-Based Materials and Its De-NOx Performance

Porous magnesium oxychloride cement (PMOC) has a high specific surface area formed by interlocking whiskers, which can be used as a promising photocatalyst substrate for the photocatalytic removal of atmospheric pollutants. In this paper, magnesium oxychloride cement (MOC) was used as matrix and TiO2 as catalyst to prepare MOC blocks. Plant-based protein was used as a foaming agent to form the layered porous structure suitable for supporting TiO2 particles, which effectively increased the surface area of light radiation and TiO2 adhesion area in photocatalytic porous magnesium oxychloride cement (PPMOC). It was found that the addition of the foaming agent can increase the adsorption capacity of MOC to TiO2. The vacuum-immersion loading method can effectively support TiO2 on the surface of PMOC. The photocatalytic performance of PPMOC can be improved by multiple loading, while higher porosity of PMOC would reduce the loading surface of matrix to TiO2 particles, which might decrease the photocatalytic efficiency. As can be observed in PPMOC specimens, when the porosity of PPMOC is less than 60%, increasing the porosity can improve the photocatalytic efficiency, while when the porosity is higher than 60%, increasing the porosity decreased the photocatalytic efficiency due to the reduction of the loading surface. The excellent nitrate selectivity of PPMOC also shows good application potential in the field of catalytic degradation of nitrogen oxides.

THE PORE SIZE-DEPENDENT FRACTALITY OF POROUS STRUCTURE IN CEMENT PASTE: ANALYSIS, MODELING AND APPLICATIONS

The fractal characteristic of cement paste has been investigated for decades. In this paper, a systematic study referring to analysis, modeling as well as application is presented with respect to the pore size-dependent fractality of the porous structure in cement paste. In particular, the multiscale fractal dimensions other than the traditional single fractal dimension are analyzed for a measure of incomplete fractality. Then, the multiscale solid mass fractal model is introduced and implemented. It is demonstrated that the modeled pore size distribution agrees well with that obtained from the experimental measurement. Moreover, in combination with other analytical (the effective medium theory) and/or numerical (the finite element method) tools, such a pore size-dependent fractality could provide a fast assessment of some basic mechanical and physical properties.

Physicochemical property and cytocompatibility of HyA-PEG loaded PMMA based bone cement

Polymethylmethacrylate (PMMA) has been widely used as a biomaterial for orthopedic applications. However, the major complications of this bone cement are the increased fracture rate of the adjacent vertebral bodies and the elevated polymerization temperature. The primary aim of this study was to investigate the effect of PMMA bone cement in the presence of gel phase in terms of superior mechanical and cellular characteristics. Porous PMMA cement was prepared by using a Hyaluronic acid (HyA) and Polyethyleneglycol (PEG) which act as an aqueous gel phase and provide a major contribution for pore formation. Simulated body fluid (SBF) treatment on cements showed the compressive strength and elastic modulus of PMMA-10%HyA-10%PEG was significantly decreased from ∼22 MPa to ∼16 MPa and ∼159 MPa to ∼135 respectively. The degradation behaviour results revealed after SBF treatment showed porous formation. In addition, aqueous gel reduced the polymerization temperature from ∼63 °C to ∼52 °C. The aqueous gel phase did not affect apatite formation and maintained nearly physiological pH. Further in-vitro cellular activities ensured the biocompatibility and osteogenic potential of PMMA-10%HyA-10%PEG. These results suggest that PMMA-10%HyA-10%PEG bone cements possess distinctive mechanical and physicochemical properties, and are suitable cement for cellular functionalities.

Compaction Behavior and Damage Constitutive Model for Porous Cement Mortar under Uniaxial Cyclic Loads.

The void compression stage causes porous cement mortar to present special mechanical properties. In order to study the compaction behavior and the damage evolution of the porous material, cement mortar specimens with an average porosity of 26.8% were created and cyclic uniaxial compression tests were carried out. The irreversible strain accumulated in the tests was obtained by cyclic loading and unloading. As the secant modulus of the porous cement mortar increases with stress in the pre-peak deformation stage, its damage variable is defined according to the accumulated irreversible strain instead of modulus degradation. The strain-based damage indicator fitted with the damage evolution law is characterized by linear accumulation at the beginning and has an acceleration rate of about 0.3 in the pre-peak deformation stage, and the damage value converges to 1 at failure. Based on the Weibull distribution, a constitutive damage model of porous cement mortar is improved by considering both the damage evolution during the plastic deformation stage and the mechanical behavior in the compaction stage. The theoretical envelope curves obtained by the constitutive model are in good agreement with the experimental envelope curves of cyclic uniaxial compression in the compaction and pre-peak stages, and the average absolute error is about 0.54 MPa in the entire pre-peak stage, so the proposed damage constitutive model can characterize the damage-induced mechanical properties of porous cement mortar in the compaction and pre-peak stages.

Recombinant human bone morphogenetic protein 2/porous calcium phosphate cement/autologous bone and combination of platelet-rich plasma in repairing of large bone defects in rabbits by Masquelet technique

To investigate the optimal mixing ratio of recombinant human bone morphogenetic protein 2 (rhBMP-2) with porous calcium phosphate cement (PCPC) and autologous bone as bone grafting material for the repair of large bone defects using Masquelet technique. The effect of platelet-rich plasma (PRP) on the healing of bone defects was evaluated under the optimal ratio of mixed bone. Fifty-four New Zealand White rabbits were taken to establish a 2 cm long bone defect model of the ulna and treated using the Masquelet technique. Two parts of the experiment were performed in the second phase of the Masquelet technique. First, 36 modeled experimental animals were randomly divided into 4 groups ( n=9) according to the mass ratio of autologous bone and rhBMP-2/PCPC. Group A: autologous bone (100%); group B: 25% autologous bone+75% rhBMP-2/PCPC; group C: 50% autologous bone+50% rhBMP-2/PCPC; group D: 75% autologous bone+25% rhBMP-2/PCPC. The animals were executed at 4, 8, and 12 weeks postoperatively for general observation, imaging observation, histological observation (HE staining), alkaline phosphatase (ALP) activity assay, and biomechanical assay (three-point bending test) were performed to assess the osteogenic ability and to determine the optimal mixing ratio. Then, 18 modeled experimental animals were randomly divided into 2 groups ( n=9). The control group was implanted with the optimal mixture ratio of autologous bone+rhBMP-2/PCPC, and the experimental group was implanted with the optimal mixture ratio of autologous bone+rhBMP-2/PCPC+autologous PRP. The same method was used to observe the above indexes at 4, 8, and 12 weeks postoperatively. The bone healing process from callus formation to the cortical connection at the defected gap could be observed in each group after operation; new bone formation, bridging with the host bone, and bone remodeling to normal bone density were observed on imaging observation; new woven bone, new capillaries, bone marrow cavity, and other structures were observed on histological observation. The ALP activity of each group gradually increased with time ( P<0.05); the ALP activity of group A was significantly higher than that of the other 3 groups at each time point after operation, and of groups C and D than group B ( P<0.05); there was no significant difference between groups C and D ( P>0.05). Biomechanical assay showed that the maximum load in three-point bending test of each group increased gradually with time ( P<0.05), and the maximum loads of groups A and D were significantly higher than that of groups B and C at each time point after operation ( P<0.05), but there was no significant difference between groups A and D ( P>0.05). According to the above tests, the optimal mixing ratio was 75% autogenous bone+25% rhBMP-2/PCPC. The process of new bone formation in the experimental group and the control group was observed by gross observation, imaging examination, and histological observation, and the ability of bone formation in the experimental group was better than that in the control group. The ALP activity and maximum load increased gradually with time in both groups ( P<0.05); the ALP activity and maximum load in the experimental group were significantly higher than those in the control group at each time point after operation ( P<0.05), and the maximum load in the experimental group was also significantly higher than that in group A at 12 weeks after operation ( P<0.05). In the second phase of Masquelet technique, rhBMP-2/PCPC mixed with autologous bone to fill the bone defect can treat large bone defect of rabbit ulna, and it has the best osteogenic ability when the mixing ratio is 75% autologous bone+25% rhBMP-2/PCPC. The combination of PRP can improve the osteogenic ability of rhBMP-2/PCPC and autologous bone mixture.

Preparation and Hardened Performance of Bentonite-Induced Porous Magnesium Oxysulfate Cement Paste.

Porous magnesium oxysulfate (MOS) cement pastes were successfully fabricated by injecting presaturated bentonite into modified MOS cement paste. Their pore structure and hardened performance were investigated. The results indicated that the 20MgO-MgSO4·7H2O-18H2O system modified by citric acid (C6H8O7⋅H2O) and ethylene diamine tetraacetic acid was suitable to fabricate porous MOS cement paste. Bentonite slurry led to significant refinement of pores, generating nanosized pores in MOS cement pastes. When volume replacement of bentonite slurry in MOS cement paste rose between 0 and 60%, pore size corresponding to the peak in the pore size distribution curve of MOS cement-based materials decreased from 180.0 nm to 22.8 nm and then increased to 163.0 nm, and the porosity linearly increased from 21.1% to 58.1%. These small pores caused the successful preparation of porous MOS cement paste with dry bulk density of 760–1650 kg/m3, compressive strength of 7.8–69.8 MPa, and thermal conductivity of 0.25–0.85 W/(m·K).

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ТА МЕТОДИ ПІДБОРУ СКЛАДУ ПОРИСТОГО ЦЕМЕНТОБЕТОНУ

Introduction. The construction and operation of airfield elements such as runways, taxiways, and parking places that meet the requirements of regulations and modern methods of road works are significant in the system of aviation security in modern conditions. In order to ensure safe conditions for landing aircraft on the runway during downpours and heavy rains, porous cement concrete should be used as the surface source, which will further reduce hydroplaning. Research problem. Due to a large number of aircraft crashes and their rolling outside the runway, which is associated with the frequent failure of the coating to perform drainage because of unfavorable weather conditions (including thunderstorms, showers, and snowfalls), there is the need to improve the existing structures of airfield pavements or to develop new technologies to improve the drainage of pavement and, accordingly, the safety of takeoff and landing of aircraft on the runway. The use of modern airfield pavement structures made of porous cement concrete with drainage properties is one of the ways to solve this problem. The purpose of the study. The research aims to prove that the use of porous cement concrete in mathematical modeling of porous cement concrete composition and improvement of airfield structure will guarantee safe conditions for takeoff and landing and taxiing of aircraft on the runway. Materials and methods. During the research, the analysis of monographs, normative documentation, methodical instructions and recommendations was made. These documents establish requirements concerning the selection of materials for porous cement concrete structure, its use in the construction of elements of an airfield, and their exploitation. Results. The feasibility of using different methods of design and selection of the design and selection of porous cement concrete is proved. Conclusion. The revision and analysis of the literature showed that in order to obtain products and structures with specified properties the most appropriate approach is the use of several methods simultaneously to project and select components for the composition of porous cement concrete. The benefits of the simultaneous use of several methods such as the reduction of information processing time, the improvement of mixture quality, the flexibility of the model to adjustment, the simplification of analysis, and the comparison of indicators of mathematical modeling and laboratory tests were highlighted.

Investigation on frost heaving stress (FHS) of porous cement concrete exposed to freeze-thaw cycles

Frost Heaving Stress (FHS) is one of the main causes of freeze-thaw (FT) damage in porous cement concrete. This study customized a device for the measurement of FHS in the laboratory. Firstly, rodding, vibration, and static compaction methods were compared for the preparation of porous cement concrete in terms of the air void characteristics and air void distribution. Based on the proposed measurement device, the influence of curing time, air void, saturation degree, and freeze-thaw cycles on the FHS evolution were discussed, respectively. Besides, the release characteristics of FHS in the thawing process were also characterized. The results indicated that the evolution of FHS in the freezing process can be divided into three stages that accounted for the thermal contraction, phase transformation of water, and the end of phase transformation. The FHS of porous cement concrete can be reduced through the extension of curing or reduction of air void content. In general, the increase of saturation degree induced the growth of FHS. With respect to the release characteristics of FHS, the FHS would not completely dissipate and the remaining FHS would accumulate as the F-T cycle increased.

Triaxial behavior of a stabilized and a highly porous oil well cement paste at different saturation and drainage conditions

Well cement is the most common barrier material in wells for geothermal and hydrocarbon production. As cements are exposed to hydrostatic loads and periods of deviatoric loading in wellbore environments, it is important to understand the mechanical behavior of cement under relevant conditions. We study effects of porosity, saturation, confining pressure and drainage conditions on the mechanical behavior of class G well cement using two basic formulations, one which produces a highly porous cement paste. The high-porosity cement exhibited lower strength and reduced elastic moduli compared to the stabilized formulation. The elastic moduli for both formulations were reduced with increasing confining pressure, and the most pronounced effect of confinement was increased ductility and pronounced strain hardening behavior of the two cements, likely due to compaction. Under saturated and undrained conditions, the stabilized cement exhibited an increase in stiffness and essentially brittle failure even at 20 MPa confining pressure. The porous cement showed less sensitivity to drainage conditions. We attribute this observation to possible generation of internal micro-cracks and dislocations instead of a macroscopic failure plane. The results contribute to increased understanding of the mechanical response of conventional and porous cements under relevant confining pressures and different saturation and drainage conditions.

Environmental Friendly Fabrication of Porous Cement Membranes via Reusable Camphene-Based Freeze-Casting Method.

Inorganic membranes have been developed rapidly in recent years because of excellent anti-fouling performance, high mechanical strength and outstanding resistances to acid and alkali. However, the high production cost still restricts its large-scale industrial application. In this work, an environmental friendly unidirectional freezing method via introducing camphene as a reusable template was adapted to prepare porous cement membranes (PCMs). The naturally formed and highly aligned porous structures of PCMs could be divided into three parts: a dense layer, a transition layer and a supporting layer. With the solid content rising from 40 wt.% to 60 wt.%, the pore size of the PCMs decreased from 3.34 nm to 3.62 nm, the bovine serum albumin (BSA) rejection increased from 81.3% to 93.5% and water flux decreased from 346.8 L·m−2·h−1 to 167.3 L·m−2·h−1 (0.2 MPa). Significantly, the performance of PCMs was maintained; even the camphene was reused 20 times. Additionally, the recovery rate of camphene could be reached up to 97.16%. Therefore, this method is cost effective and environmental friendly, which endowed the PCMs great potential in water treatment.

Preparation of Porous Silicate Cement Membranes via a One-Step Water-Based Hot-Dry Casting Method.

A commercial interest in the improvement in the separation performance and permeability of porous materials is driving efforts to deeply explore new preparation methods. In this study, the porous silicate cement membranes (PSCMs) were successfully prepared through an adjustable combination of hot–dry casting and a cement hydration process. The obtained membrane channel was unidirectional, and the surface layer was dense. The physical characteristics of the PSCMs including their pore morphology, porosity, and compressive strength, were diversified by adjusting the solid content and hot–dry temperature. The results indicated that with the solid content increasing from 40 wt. % to 60 wt. %, the porosity decreased by 8.07%, while the compressive strength improved by 12.46%. As the hot–dry temperature increased from 40 °C to 100 °C, the porosity improved by 23.04% and the BET specific surface area and total pore volume enlarged significantly, while the compressive strength decreased by 27.03%. The pore size distribution of the PSCMs exhibited a layered structure of macropores and mesopores, and the pore size increased with the hot–dry temperature. Overall, the PSCMs, which had typical structures and adjustable physical characteristics, exhibited excellent permeability and separation performance.

A Workability Characterization of Innovative Rubber Concrete as a Grouting Material.

The aim of this study is to assess the workability of an innovative rubber concrete to fill in the gaps in a shield tunnel construction. This grouting material includes porous sand, PVA (polyvinyl alcohol) fiber, cement, and rubber. One advantage of the material is its high toughness, which is good for the postfailure stage of an earthquake event. Evaluations were carried out on the physical properties in terms of the slurry density, consistency, fluidity, bleeding rate, consolidation shrinkage rate, setting time, and unconfined compressive strength (UCS) (i.e., 3 and 28 days). The toughness index was also introduced to evaluate the performance at the postfailure stage. The results demonstrate that the toughness index will increase as the rubber content increases. It increases from 1.0 at 0% to 1.7 at 80% rubber content (28 days’ curing) and from 1.2 at 0% to 2.2 at 80% rubber content (3 days’ curing). The increase in fiber content and fiber length will also increase the toughness index as the fiber will enhance the tensile strength of the matrix. The results show that when the fiber content increases from 0% to 1%, the toughness index increases from 1 to 7 (28 days’ curing) and from 1.1 to 10 (3 days’ curing). Similarly, if the fiber content or fiber length is above the optimum level, the UCS of the material will be compromised. The optimum fiber content is 0.8%, and the optimum fiber length is 6 mm to 9 mm. This study suggests that the balance of physical properties should be considered in designing a satisfactory grouting material based on the specific purpose of the engineering practice.

Investigation on high-temperature stability of recycled aggregate asphalt mixture based on microstructural characteristics

Construction and demolition wastes (CDW) are a complex mixture containing cement mortar and mineral aggregate. Recycled aggregate (RA) is a production of CDW after the crushing process. The presented study efforts mainly focus on the influence of RA content on the high-temperature stability of RAAM, but the analysis of the RA morphology effect is still lacking. Giving microstructural insight into the impacts of RA on the high-temperature failure of RAAM is beneficial in promoting the utilization of CDW in pavement engineering. In this paper, RAAM with different RA contents was firstly designed by the Marshall method, and the mechanical properties of RAAM at high temperatures were investigated using a uniaxial penetration test (UPT). Then, high-precision spatial models of RA particles were reconstructed based on CT images, and four indicators were introduced to quantify the RA macro shape and micro-morphology through spatial model data. Furthermore, the relationships between shear resistance of RAAM and RA morphology were established according to UPT test results and spatial model indicators. Finally, an X-ray CT saner was employed to track the evolution of microstructure damage before and after compressive deformation. Results show that the attached cement mortar is the primary resource of pores in RA particles, and pores volume and number in RA particles are random. Compared with natural aggregate, RA particle has more complicated morphological characteristics due to its porous cement mortar. The complex morphology and attached porous cement mortar of RA particles significantly affect the asphalt mixture high-temperature stability. Using RA particles causes more structural failures in RAAM during high-temperature deformation, and the damage inside cement mortar and interface with asphalt mortar are the primary resources of failure. This study shows that RA with content less than 50% can be an effective alternative for natural aggregate when considering the high-temperature stability of RAAM.

Injectable bone cement containing carboxymethyl cellulose microparticles as a silver delivery system able to reduce implant-associated infection risk

In the challenging quest for a solution to reduce the risk of implant-associated infections in bone substitution surgery, the use of silver ions is promising regarding its broad spectrum on planktonic, sessile as well as multiresistant bacteria. In view of controlling its delivery in situ at the desired dose, we investigated its encapsulation in carboxymethyl cellulose (CMC) microparticles by spray-drying and included the latter in the formulation of a self-setting calcium phosphate bone cement. We implemented an original step-by-step methodology starting from the in vitro study of the antibacterial properties and cytotoxicity of two silver salts of different solubility in aqueous medium and then in the cement to determine the range of silver loading able to confer anti-biofilm and non-cytotoxic properties to the biomaterial. A dose-dependent efficiency of silver was demonstrated on the main species involved in bone-implant infection (S. aureus and S. epidermidis). Loading silver in microspheres instead of loading it directly inside the cement permitted to avoid undesired silver-cement interactions during setting and led to a faster release of silver, i.e. to a higher dose released within the first days combining anti-biofilm activity and preserved cytocompatibility. In addition, a combined interest of the introduction of about 10% (w/w) silver-loaded CMC microspheres in the cement formulation was demonstrated leading to a fully injectable and highly porous (77%) cement, showing a compressive strength analogous to cancellous bone. This injectable silver-loaded biomimetic composite cement formulation constitutes a versatile bone substitute material with tunable drug delivery properties, able to fight against bone implant associated infection. Statement of significanceThis study is based on two innovative scientific aspects regarding the literature: i) Choice of silver ions as antibacterial agent combined with their way of incorporation: Carboxymethylcellulose has never been tested into bone cement to control its drug loading and release properties. ii) Methodology to formulate an antibacterial and injectable bone cement: original and multidisciplinary step-by-step methodology to first define, through (micro)biological tests on two silver salts with different solubilities, the targeted range of silver dose to include in carboxymethylcellulose microspheres and, then optimization of silver-loaded microparticles processing to fulfill requirements (encapsulation efficiency and size). The obtained fully injectable composite controls the early delivery of active dose of silver (from 3 h and over 2 weeks) able to fight against bone implant-associated infections.