Apesar do avanço tecnológico crescente na construção civil, a falta de durabilidade das estruturas de concreto, tanto em edificações como pavimentação, tem sido constatada com acentuada assiduidade e proporção. O compósito cimentício de elevada deformação, também conhecido como Engineered Cementitious Composites (ECC), foi difundido a partir do conceito de concretos de alto desempenho reforçado com fibras, visando suprir o comportamento frágil do concreto convencional e problemas relacionados à falta de durabilidade gerada, principalmente, devido à propagação de fissuras. Neste contexto, o Laboratório de Ensaio de Modelos Estruturais (LEME) da Universidade Federal do Rio Grande do Sul (UFRGS) consolidou, nos últimos cinco anos, um grupo de pesquisa voltado ao estudo do ECC aliado a utilização de materiais nacionais. A concepção tem sido baseada na aplicação de materiais que proporcionem custos mais baixos e fomentem questões de sustentabilidade ambiental. Assim, foram incorporados ao material, fibra de polipropileno (2% em volume) e substituição parcial do cimento por 30% (em volume) de cinza de casca de arroz residual. O presente trabalho visa analisar questões de durabilidade destes compósitos (com e sem a incorporação de cinza), e compará-los a concretos convencionais, através de ensaios relacionados ao estudo da estrutura de poros (absortividade, absorção e índice de vazios, absorção e água por capilaridade, absorção de água pelo método do cachimbo e microscopia eletrônica de varredura), penetração e difusão de íons cloretos, retração livre e restringida, e, por fim, resistência à abrasão. Os resultados obtidos indicam que a incorporação de cinza de casca de arroz melhorou significativamente as propriedades do compósito relacionadas à conexão e solução dos poros, dificultando a passagem de cloretos, além de apresentar resistência à abrasão semelhante ao compósito de referência. Sua desvantagem está relacionada às maiores aberturas de fissuras ocasionadas devido à retração restringida. Entretanto, o trabalho evidencia a viabilidade e vantagem do uso de cinza de casca de arroz na produção do compósito, em termos de durabilidade. / Despite the increasing technological advances in construction, the lack of concrete structures durability, both in buildings and pavement, have been found with severe attendance and proportion. The high strain cementitious composite, also known as Engineered Cementitious Composites (ECC), was widespread from the concept of high performance fiber reinforced concrete, in order to supply the fragile behavior of conventional concrete and problems related to lack of durability generated mainly due to crack propagation. In this context, the Laboratório de Ensaios e Modelos Estruturais (LEME) of the Federal University of Rio Grande do Sul (UFRGS) consolidated over the last five years, a research group focused on the ECC study allied with the use of national materials. The design has been based on the application materials that provide lower costs and promote environmental sustainability issues. Thus, they were incorporated into the material polypropylene fibers (2% by volume) and partial cement replacement of 30% (by volume) of residual rice husk ash. This study aims to examine durability issues of these composites (with and without rice husk ash), and compare them to conventional concretes, through tests related to the study of pore structure (absorptivity, absorption and void ratio, water absorption by capillarity, water absorption by the pipe method and scanning electron microscopy), penetration and diffusion of chloride ions, free and restrained shrinkage, and, finally, abrasion resistance. The results indicate that the incorporation of rice husk ash significantly improved material properties related to connection and pores solution, hindering the chloride ingress, and presents abrasion resistance similar to the reference composite. Its disadvantage is related to the larger cracks due to restrained shrinkage. However, the work demonstrates the viability and advantage of use rice husk ash in the composite production in terms of durability.

A utilização de fibras vegetais como reforço de matrizes frágeis de cimento é justificada pelo baixo custo, alta disponibilidade, principalmente em países como o Brasil, que possui agricultura desenvolvida, boas condições edafo-climáticas e grandes áreas para cultivo. No entanto, em razão da alta alcalinidade do cimento a matriz reforçada tem a durabilidade comprometida pela degradação das fibras. Uma medida para minimizar esse ataque alcalino é a dissolução da lignina e da hemicelulose das fibras, menos resistentes em condições de pH elevado, através da polpação química, processo que individualiza as fibras celulósicas, que podem ser utilizadas como reforço de compósitos cimentícios em substituição parcial às fibras sintéticas. As polpas aplicadas para este fim são comumente produzidas pelo processo Kraft. Uma alternativa mais limpa a este processo é a polpação organossolve que usa reagentes orgânicos durante o cozimento e proporciona facilidade para recuperação do solvente no final do processo. O bambu possui fibras de elevada resistência mecânica, portanto sua utilização como matéria-prima para produção de polpas celulósicas é justificada por ser um material viável, de fácil aplicação, rápido crescimento e pronta disponibilidade. A proposta deste trabalho foi a produção de polpa de bambu pelo processo organossolve utilizando as variáveis tempo x temperatura com a finalidade de encontrar a condição ótima para o processo, de forma que houvesse melhor rendimento e que as características químicas, físicas e morfológicas da polpa fossem compatíveis às exigidas para utilização como reforço de matrizes cimentícias. A melhor condição foi o cozimento a temperatura de 190ºC durante 2 h. O tempo de 1 h de cozimento foi insuficiente para a solubilização da lignina e o período de 3 h é inviável devido a degradação da cadeia de celulose. Foram produzidos pelo método de sucção a pressão negativa, compósitos com matriz de cimento com substituição parcial de metacaulim e testados os teores de 6, 8, 10 e 12% de polpa de bambu como reforço. O teor de polpa definido como ideal foi 8%, o mesmo encontrado na literatura para polpa Kraft de bambu. Produziram-se placas com duas composições. Uma com substituição parcial de 25% do cimento por metacaulim e a segunda com substituição de 25% do cimento por calcário moído. Os compósitos contendo metacaulim foram submetidos a envelhecimento acelerado por meio de 50, 100 e 200 ciclos de imersão e secagem para avaliação da durabilidade. As propriedades físicas foram melhoradas com os ciclos de envelhecimento, ocasionando diminuição na porosidade aparente pela migração dos produtos da hidratação do cimento para a zona em torno das fibras, e, em consequência, melhorias nas propriedades mecânicas de módulo de ruptura (MOR), limite de proporcionalidade (LOP) e módulo de elasticidade (MOE), tanto para a substituição parcial do cimento por metacaulim como para calcário. Houve diminuição na energia específica (EE) com os ciclos de imersão e secagem, justificada pela maior aderência entre fibra-matriz. Observados os parâmetros de polpação organossolve adotados para o bambu, essa polpa apresenta-se viável para reforço de matrizes inorgânicas a base de cimento Portland. / The use of natural fibers as reinforcement for brittle cement matrices is justified by the its low cost, high availability, especially in countries like Brazil, which has developed agriculture, good soil and climatic conditions and large areas for cultivation. However, due to the high alkalinity of cement the reinforced matrix has it durability compromised by the fiber degradation. One measure to minimize this alkaline attack is the dissolution of lignin and hemicellulose fibers, that are less resistant under conditions of high pH, by chemical pulping, that is a process that individualizes the cellulosic fibers, which can be used as reinforcement of cementitious composites in partial replacement synthetic fibers. The pulps applied for this purpose are commonly produced by the kraft pulping process. A cleaner alternative to this process is the organosolv pulping that use organic reagents during cooking and provides facility for solvent recovery at the end of the process.The bamboo fibers have high mechanical strength, therefore their use as raw materials for production of cellulose pulps is justified because it is a viable material, easily applied, rapid growth and ready availability. The purpose of this study was the production of bamboo pulp by the organosolv process using the variables time vs temperature in order to find the optimum condition for the process, so that there was a better yield and that the chemical, physical and morphological characteristics of the pulp were compatible to those required for use as reinforcement in cementitious matrices. The best condition was the cooking temperature of 190ºC for 2 h. The time of 1 h of cooking was insufficient to solubilize the lignin and the time of 3 h is infeasible due to degradation of the cellulose chain. The composites with matrix of cement and with partial replacement of metakaolin were produced by the method of negative pressure suction and tested the levels of 6, 8, 10 and 12% bamboo pulp as reinforcement. The pulp content was defined as an ideal 8%, as found in the literature for bamboo Kraft pulp. The plates were produced with two compositions. One with partial substitution of cement by 25% of metakaolin and the second with 25% replacement of cement by limestone. The composites containing metakaolin were subjected to accelerated ageing through 50, 100 and 200 wet and dry cycles for durability evaluation. The physical properties were improved with the ageing cycles, decreasing the porosity by migration of the cement hydration products to the zone around the fibers and, consequently, improvements in mechanical properties of modulus of rupture (MOR), limit proportionality (LOP) and modulus of elasticity (MOE) for both the partial replacement of cement by metakaolin as for limestone. The decreased of the specific energy (EE) with the wet and dry cycles was due to the higher adhesion between fiber-matrix. With the observation of the parameters adopted for bamboo organosolv pulping, this pulp has to be feasible for reinforcement of inorganic matrices based in Portland cement.

The rheological behavior analysis of Engineered Cementitious Composites (ECC) is key to understand how the different preparation techniques affect the composite mechanical performance. However, the rheological assessment of reinforced materials becomes more complex since fibers usually cause flow disturbances not found in nonreinforced cementitious materials. Besides that, simple workability measurement techniques are not able to fully understand the composite behavior in the fresh state creating the need for more precise techniques to be employed. The main objectives of this study were to evaluate the ECC rheological behavior using different rheometer devices (Vane system and Ball measuring system) and investigate the influence of mixing processes on the fiber homogenization and rheological behavior. Additionally to this, a link between rheological behavior and mechanical performance was investigated. In the end, the ball measuring system revealed to be more efficient than the vane system when evaluating the composite rheological behavior. In addition, the mixing process influenced the rheological behavior of PVA-ECC especially regarding the moment which fibers are added. Fiber addition after mortar mixture improved fibers homogenization and reduced mixing energy by around 8%. Moreover, a correlation between rheological and mechanical properties showed that a 2-times variation in either yield stress or viscosity can lead to a variation of more than 50% in flexural strength without significantly affecting the composite compressive strength. It was also found that the lower the composite yield stress and viscosity the higher was its ultimate strain. To conclude, all those parameters contributed to understand the composite rheological behavior and globally optimize its performance. / Sem resumo

<div><div><div><p>The exceptional long-term performance of concrete is a primary reason that this material represents a significant portion of the construction industry. However, a portion of this construction material is prone to premature deterioration for multi-physical durability issues such as internal frost damage, restrained shrinkage damage, and aggregate susceptibility to fracture. Since each durability issue is associated with a unique damage mechanism, this study aims at investigating the underlying physical mechanisms individually by characterizing the mechanical and thermal properties development and indicating how each unique damage mechanism may compromise the properties development over the design life of the material.</p><p>The first contribution of this work is on the characterization of thermal behavior of porous media (e.g., cement-based material) with a complex solid-fluid coupling subject to thermal cycling. By combining Young-Kelvin-Laplace equation with a computational heat transfer approach, we can calculate the contributions of (i) pore pressure development associated with solidification and melting of pore fluid, (ii) pore size distribution, and (iii) equilibrium phase diagram of multiple phase change materials, to the thermal response of porous mortar and concrete during freezing/thawing cycles. Our first finding indicates that the impact of pore size (and curvature) on freezing is relatively insignificant, while the effect of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to -35 °C). Our second finding shows that porous cementitious composites containing lightweight aggregates (LWAs) impregnated with an organic phase change material (PCM) as thermal energy storage (TES) agents have the significant capability of improving the freeze-thaw performance. We also find that the phase transitions associated with the freezing/melting of PCM occur gradually over a narrow temperature range (rather than an instantaneous event). The pore size effect of LWA on freezing and melting behavior of PCM is found to be relatively small. Through validation of simulation results with lab-scale experimental data, we then employ the model to investigate the effectiveness of PCMs with various transition temperatures on reducing the impact of freeze-thaw cycling within concrete pavements located in different regions of United States.</p><div><div><div><p>The second contribution of this work is on quantification of mechanical properties development of cementitious composites across multiple length scales, and two damage mechanisms associated with aggregate fracture and restrained shrinkage cracking that lead to compromising the long-term durability of the material. The former issue is addressed by combining finite element method-based numerical tools, computational homogenization techniques, and analytical methods, where we observe a competing fracture mechanism for early- age cracking at two length scales of mortar (meso-level) and concrete (macro-level). When the tensile strength of the cement paste is lower than the tensile strength of the aggregate phase, the crack propagates across the paste. When the tensile strength of the cement paste exceeds that of the aggregate, the cracks begin to deflect and propagate through the aggregates. As such, a critical degree of hydration (associated with a particular time) exists below which the cement paste phase is weaker than the aggregate phase at the onset of hydration. This has implications on the inference of kinetic based parameters from mechanical testing (e.g., activation energy). Next, we focus on digital fabrication of a cement paste structure with controlled architecture to allow for mitigating the intrinsic damage induced by inherent shrinkage behavior followed by extrinsic damage exerted by external loading. Our findings show that the interfaces between the printed filaments tend to behave as the first layer of protection by enabling the structure to accommodate the damage by deflecting the microcrack propagation into the stable configuration of interfaces fabricated between the filaments of first and second layers. This fracture behavior promotes the damage localization within the first layer (i.e., sacrificial layer), without sacrificing the overall strength of specimen by inhibiting the microcrack advancement into the neighboring layers, promoting a novel damage localization mechanism. This study is undertaken to characterize the shrinkage-induced internal damage in 7-day 3D-printed and cast specimens qualitatively using X-ray microtomography (μCT) technique in conjunction with multiple mechanical testing, and finite element numerical modeling. As the final step, the second layer of protection is introduced by offering an enhanced damage resistance property through employing bioinspired Bouligand architectures, promoting a damage delocalization mechanism throughout the specimen. This novel integration of damage localization-delocalization mechanisms allows the material to enhance its flaw tolerant properties and long-term durability characteristics, where the reduction in the modulus of rupture (MOR) of hardened cement paste (hcp) elements with restrained shrinkage racking has been significantly improved by ~ 25% when compared to their conventionally cast hcp counterparts.</p></div></div></div></div></div></div>

No / The objective of this study was to evaluate the effect of corrosion level on shear behavior of engineered cementitious composite (ECC) beams. Reinforced normal concrete (R-NC) specimens with compressive strength equal to the ECC specimens were also used for control purposes. Ten reinforced concrete beams (five ECC and five NC) with dimensions of 150 x 220 x 1400 mm (5.91 x 8.66 x 55.12 in.) were manufactured for the study. Using accelerated corrosion through the application of a constant current of 1 ampere, four levels of corrosion were established at 5%, 10%, 15%, and 20% of mass loss of the reinforcing bars. To ensure the highest probability of shear failure mode, all beams were tested under a four-point loading system with a shear span-effective depth ratio of 2.5. General structural behavior, strength, stiffness, failure mode, and energy absorption capacities of ECC and R-NC beams subjected to different corrosion levels were evaluated and compared. Experimental results showed a high correlation between calculated mass loss and measured mass loss in reinforcing bars due to accelerated corrosion. Compared to NC, ECC beams exhibited significantly higher strength, stiffness, and energy absorption capacity, along with superior performance in terms of the restriction of damage caused due to corrosion. The increase in corrosion level negatively influenced the structural behavior of the ECC beams tested.

Yes / In view of high-performance, multifunctional and low-carbon development of infrastructures, there is a growing demand for smart engineering materials, making infrastructures intelligent. This paper reports a new-generation self-sensing cementitious composite (SSCC) incorporated with a hierarchically structured carbon fiber-carbon nanotube composite filler (CF-CNT), which is in-situ synthesized by directly growing CNT on CF. Various important factors including catalyst, temperature, and gas composition are considered to investigate their kinetic and thermodynamic influence on CF-CNT synthesis. The reciprocal architecture of CF-CNT not only alleviates the CNT aggregation, but also significantly improves the interfacial bonding between CF-CNTs and matrix. Due to the synergic and spatially morphological effects of CF-CNT, i.e., the formation of widely distributed multiscale reinforcement networks, SSCCs with CF-CNTs exhibit high mechanical properties and electrical conductivity as well as excellent self-sensing performances, particularly enhanced sensing repeatability. Moreover, the SSCCs with CF-CNTs are integrated into a full-scale maglev girder to devise a smart system for crack development monitoring. The system demonstrates high sensitivity and fidelity to capture the initiation of cracks/damage, as well as progressive and sudden damage events until complete failure of the maglev girder, indicating its considerable potential for structural health monitoring of infrastructures. / The work described in this paper is supported by grants from the National Science Foundation of China (51978127 and 51578110) and grants from the China Postdoctoral Science Foundation (2022M710973 and 2022M720648).

No / Incorporating nanomaterials brings great changes in tailoring the nano-/micro-/macroscale structures of bulk cement paste phase and interfacial transition zone in the cementitious composites through the nano-core effect, thus achieving stronger, more durable, and smart/multi-functional cementitious composites. Owing to the nano-modification of cement paste in combination with the supplement of nanoscale continuity for multiscale raw materials of cementitious composites, nanomaterials gradually show the potential to become the indispensable seventh component of cementitious composites besides cement, water, fine aggregates, coarse aggregates, chemical additives, and mineral additives. Therefore tailoring cementitious composites with nanomaterials provides a promising approach to develop the new generation of cementitious composites (e.g., ultra-high performance, smart/multi-functional, and resilient) and sustainable infrastructures. This chapter aims to provide a systematic overview of tailoring cementitious composites with various types of nanomaterials. It initially covers the principle of tailoring cementitious composites with nanomaterials and dispersion of nanomaterials in cementitious composites. It then presents the properties of cementitious composites with 0D, 1D, and 2D nanomaterials, namely, hydration, rheology, workability, durability, functional, and mechanical properties. It also highlights various applications of cementitious composites with nanomaterials, including structural health monitoring, traffic detection, and pollutant purification. This chapter concludes by presenting the future prospects of cementitious composites with nanomaterials.

Yes / Cementitious composites are generally brittle and develop considerable tension cracks, resulting in corrosion of steel reinforcement and compromising structural durability. With careful selection and treatment, some kinds of bacteria are able to precipitate calcium carbonate and ‘heal’ cracks in cementitious composites through their metabolism, namely bacterial activity. It is envisioned that the bacterial technology-enabled cementitious composites could have great potential for engineering applications such as surface treatment, crack repair and self-healing construction material. This paper presents the state-of-the-art development of bacterial technology-enabled cementitious composites from the following aspects: mechanisms of bacterial induced calcium carbonate precipitation; methods of applying bacteria into cementitious composites; mechanical properties, durability and their influencing factors; various applications; cost effective analysis and prospect. The paper concludes with an outline of some future opportunities and challenges in the application of bacterial technology-enabled cementitious composites in construction. / National Science Foundation of China (51578110) and the Fundamental Research Funds for the Central Universities in China (DUT18GJ203).

Yes / The development of ultra-high performance cementitious composite (UHPCC) represents a significant advancement in the field of concrete science and technology, but insufficient hydration and high autogenous shrinkage relatively increase the pores inside UHPCC, in turn, affecting the macro-performance of UHPCC. This paper, initially, optimized the pore structure of UHPCC using different types and dimensions of nanofillers. Subsequently, the pore structure characteristics of nano-modified UHPCC were investigated by the mercury intrusion porosimeter method and fractal theory. Finally, the fluid permeability of nano-modified UHPCC was estimated by applying the Katz-Thompson equation. Experimental results showed that all incorporated nanofillers can refine the pore structure of UHPCC, but nanofillers with different types and dimensions have various effects on the pore structure of UHPCC. Specifically, CNTs, especially the thin-short one, can significantly reduce the porosity of UHPCC, whereas nanoparticles, especially nano-SiO2, are more conducive to refine the pore size. Among all nanofillers, nano-SiO2 has the most obvious effect on pore structure, reducing the porosity, specific pore volume and most probable pore radius of UHPCC by 31.9%, 35.1% and 40.9%, respectively. Additionally, the pore size distribution of nano-modified UHPCC ranges from 10-1nm to 105nm, and the gel pores and fine capillary pores in the range of 3-50nm account for more than 70% of the total pore content, confirming nanofillers incorporation can effectively weaken pore connectivity and induce pore distribution to concentrate at nanoscale. Fractal results indicated the provision of nanofillers reduces the structural heterogeneity of gel pores and fine capillary pores, and induces homogenization and densification of UHPCC matrix, in turn, decreasing the UHPCC fluid permeability by 15.7%-79.2%. / The authors thank the funding supported from the National Science Foundation of China (51978127, 52178188 and 51908103), the China Postdoctoral Science Foundation (2022M720648 and 2022M710973) and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039). / The full-text of this article will be released for public view at the end of the publisher embargo on 11 May 2024.

yes / In order to study the mechanical behaviors of engineered cementitious composites (ECC) reinforced with various types of polyvinyl alcohol (PVA) fibers and different fiber volume fractions after the freeze-thaw cycles, the rapid freeze-thaw method was used to test the mass loss ratios, longitudinal relative dynamic elastic modulus, compressive strength and flexural strength. The results showed that specimens incurred more serious damage with the increasing of freeze-thaw cycles; however their performance would be improved by fiber type and dosage. Mass loss rate of JPA (specimen with 2% volume content of JP fiber) was lower than JPB (specimen with 1% volume content of JP fiber). Furthermore, the mass loss rate of JPB was lower than that of CPB (specimen with 1% volume content of CP fiber). The longitudinal relative dynamic elastic modulus of JPA was higher than that of JPB while the longitudinal relative dynamic elastic modulus of JPB was higher than that of CPB. In addition, the compressive strength and flexural strength decreased with the increasing of freeze-thaw cycles. Mechanical behaviors of specimens with fiber exhibited better strength than specimens without fiber. Based on the SL 211-2006 code for the design of hydraulic structures against ice and freezing action, JPA and JPB specimens are adequate for use in severe cold regions, while specimen CPA and CPB can be used in cold regions, specimen JPC only can be used in warm regions.