Due to their exceptional electrical properties, carbon nanotubes (CNTs) can be applied as conductive fillers to develop self-sensing cement-based matrices. In order to obtain an adequate self-sensing response, CNTs must be evenly dispersed through the cement matrix in a volume sufficient enough to create an electric percolation network. This is challenged by the difficulty of dispersing CNTs; therefore, there is a demand for an efficient dispersing agent that can be filled by superplasticiezers, which are products of known compatibility with cement and high availability. This research explores the use of four commercial superplasticizers available in Brazil, both naphthalene and ether polycarboxylate-based, as dispersing agents for CNTs in water. Ultrasonic energy was applied to aqueous solutions containing CNTs and superplasticizers. UV–Vis spectroscopy and ξ-potential measurements were used to investigate which superplasticizer was more effective to disperse the CNTs. Cement pastes were produced with the CNT dispersions and their electrical resistivity was measured. It was found that only superplasticizers without aliphatic groups in their structure were capable of dispersing CNTs in water. It was concluded that second-generation naphthalene-based superplasticizers were more efficient dispersing agents for CNTs than third-generation ether polycarboxylate-based ones for self-sensing applications.

This paper reports an investigation of a very-long-term compressive-behavior evaluation of concretes containing sugarcane bagasse ash (SCBA). Initially, two different SCBA samples collected in two sugarcane plants located 1,800 km apart and 8 years apart in sampling interval were compared. From these ashes, two series of conventional and high-strength concretes were mix-designed within the Compressible Packing Model aiming for 28-day compressive strengths of 25 and 60 MPa, respectively. In the first series, a SCBA (SCBA-1) was used as a cement replacement with 10 %, 15 %, and 20 % by mass content. The different concretes were evaluated by compressive strength at 7, 28, 90, 180 days, and 1 and 10 years, and by modulus of elasticity at 28 days and 10 years. The second series of concretes was examined with similar procedures performed on the first series and another SCBA (SCBA-2, 15 % cement replacement). Compressive strength in 7, 28, 90, and 180 days, and modulus of elasticity at 28 days were evaluated. The results showed that both SCBA-1 and SCBA-2 presented similar characteristics to be considered pozzolanic materials. The effect of these ashes on the compressive strength was positive considering the cement-replacement levels used, especially for later testing ages. The results also demonstrated that all first-series concretes presented gain in compressive strength and modulus of elasticity up to 10 years of hydration. At this age, no significant differences were found in compressive strength for conventional and high-strength mixes containing SCBA compared to their respective reference mixes.

In the present paper, the thermal durability of polyvinyl alcohol fibers (PVA) was studied after fiber samples had been subjected to temperatures ranging from 90°C to 250°C. Residual mechanical properties, such as tensile strength, elastic modulus and elongation at break, and physical properties, such as density were determined. Weibull statistics were used to quantify the degree of variability in fiber strength, at the different temperature. In addition, thermal analysis of PVA fibers were carried out employing thermogravimetry and differential scanning calorimetry up to the temperature of 800°C. SEM analysis of heated and unheated samples had been carried out in order to allow the identification of the changes in the microstructure of the fibers. The degradation process of PVA fibers manifests itself in a significant loss of mass, stiffness and strength of the fibers, which is progressive with increasing temperature. Thermal analysis has shown that the melting point of PVA fibers begins at approximately 200°C and thermal degradation initiates at about 239ºC. However, progressive loss in tensile strength and elastic modulus was observed starting at a temperature as low as 90°C, due to glass transition temperature of PVA fibers at approximately 66°C. At 220°C, the elastic modulus and strength were reduced at about 45% and 52%, respectively, when compared with respective values of unheated samples. With regards to Weibull modulus, the statistical parameter did not exhibit significant influence on temperature for samples heated up to 145°C, which ranged from 23.4 to 28.8. However, samples heated to 220°C showed a sudden reduction in Weibull modulus to 8.6, indicating that a significant change occurred in the populations of fracture inducing flaws at this temperature level, which clearly affect the tensile strength and Weibull modulus.

This paper presents a solution strategy, based on a parallel Genetic Algorithm (GA), to optimize the construction of massive concrete structures. The optimization process aims at minimizing the construction cost, considering the following design variables: the concrete mixes, the placing temperature, the height of the lifts, and the time intervals between placing the lifts. The cracking tendency is taken into account by a penalty scheme imposed to the fitness function of the GA. A thermo-chemo-mechanical model is used to calculate the transient fields of hydration, temperature, stress, strain, and cracking tendency. This model is implemented in a finite element code that is, in turn, parallelized. To demonstrate the efficiency of the proposed methodology, the simulation of the construction of a structure similar to the real thick foundation of an industrial building is presented. It shows that the optimization procedure here presented is feasible and is ready to be used in real engineering applications.