Study on the Probability Distribution of Pitting for Naturally Corroded Prestressing Strands Accounting for Surface Defects

One of the most urgent scientific needs from a technical and economic engineering point of view is the assessment of concrete structures suffering corrosion deterioration. However, the pursuit of this target in the case of corroded prestressed concrete (PC) members is hindered by the lack of (i) consolidated simplified formulations to be used in the engineering daily practice and (ii) works investigating the uncertainties in the correlation between the damage induced by corrosion and the structural resistance. To this aim, the present study adopts a 3D-scanning technique for the pitting morphology evaluation of several corroded prestressing strands retrieved from 10-year-old PC beams. First, the probabilistic distributions of penetration depths have been investigated. Second, the pitting factors alpha and omega(i) have been proposed and discussed to quantify the level of corrosion in longitudinal and transversal direction, respectively. Finally, correlations have been derived between the maximum and average penetration depth as a function of the level of corrosion and the surface defects mapping has been carried out on the corroded PC beams. The results show that the penetration depth of strands subjected to chloride-induced corrosion can be best fitted by a lognormal distribution function. Additionally, the simultaneous consideration of longitudinal and transversal pitting factor is found out to be essential for an exhaustive comprehension of pitting corrosion. Moreover, the outcomes highlight that the presence of longitudinal splitting cracks plays a fundamental role in the corrosion spatial variability of prestressing strands

Fracture behavior of concretes containing MSWI vitrified bottom ash

The incorporation of waste materials into concrete allows responding to some of the most significant issues of our society: waste management and climate change. Experimental studies carried out in last decades have shown that municipal solid waste incineration (MSWI) ash, and particularly bottom ash, which constitutes the major solid by-product of incineration process, can be adopted to produce building materials. However, several issues are related to the safety and the environmental impact of MSWI ash utilization for concrete production, mainly linked with the leaching of heavy metals and toxic organic components. To solve these problems, several treatments for MSWI ash can be adopted and, among them, in this work the attention was focused on vitrification technology, which enables to convert the ash in a glassy inert solid material. The aim of the present paper is to study the feasibility of developing a “green concrete” that incorporates vitrified MSWI bottom ash as partial cement replacement, so reducing the cement content and consequently the carbon dioxide emissions as well as the raw materials consumption related to its production. The vitrified MSWI bottom ash, ground at micrometer size, was inserted into the admixtures by considering two percentages of cement substitution (10% and 20% by weight of cement). The flexural behavior of concrete containing vitrified MSWI ash was investigated through three-point bending tests under crack mouth opening displacement control. The crack path evolution was further explored by adopting the Digital Image Correlation technique. By analyzing the obtained results, it can be concluded that the use into concrete of vitrified MSWI bottom ash as cement replacement up to a percentage of 20% by weight of cement, allows reaching comparable flexural resistances with respect to the reference concrete. So, the proposed approach can represent a viable solution for the development of environmental-friendly concretes able to reduce the environmental impact of the concrete industry, which is mostly related to cement production, as known

Shear strength evaluation of RC bridge deck slabs according to CSCT with multi – layered shell elements and PARC_CL Crack Model

The shear resistance of RC slabs without shear reinforcement subjected to concentrated loads near linear support is usually calibrated on the base of tests on one – way slabs with rectangular cross section. However, the actual behavior of slabs subjected to concentrated loads is described properly by a two-way slab response. The aim of this paper consists in the evaluation of the shear resistance of bridge deck slabs using analytical formulations and Nonlinear Finite Element Analyses (NLFEA). The obtained numerical results are consequently compared with experimental observations from two test campaigns. The case studies were analysed by NLFE analyses carried out using the constitutive Crack Model PARC_CL (Physical Approach for Reinforced Concrete under Cycling Loading) implemented in the user subroutine UMAT.for in Abaqus Code. In order to predict properly global and local failure modes through a NLFE model, a multi – layered shell modelling has been used. As shell element modelling is not able to detect out – of – plane shear failures, the ultimate shear resistance of these slabs is evaluated by means of a post – processing method according to the Critical Shear Crack Theory (CSCT)

Parametric analysis on punching shear resistance of reinforced concrete continuous slabs

Punching shear resistance formulations provided by codes are usually calibrated on test results of isolated specimens that typically simulate the slab zone within the points of contraflexure around the column (hogging area). However, the behaviour of actual continuous flat slabs can be different to that of isolated specimens owing to the beneficial contributions of moment redistributions and membrane actions that cannot take place in isolated specimens. This paper presents a parametric study carried out to highlight the influence of the main geometrical features and the reinforcement layout affecting the punching shear resistance of continuous slabs around internal columns

Biochar-based cement pastes and mortars with enhanced mechanical properties

Nowadays, the environmental impact of cementitious material industry and more generally of building activities is matter of concern, especially in terms of their effects on climate change and consumption of natural resources. Within this context, the aim of this paper is the investigation of the role of biochar, a solid carbonaceous by-product material resulting from biomass pyrolysis/gasification of residual biomass, as a sustainable ingredient for the production of cementitious materials, combining carbon sink properties with enhanced mechanical properties. Although biochar is mainly investigated as agricultural amendment, there is also evidence that biochar may be a eco-friendly material to enhance the sustainable performance of cementitious materials. As outlined in literature, biochar can be used as filler to modify the nanogranular nature of cement matrix, or as substitute of clinker to reduce the emissions of greenhouse gases related to cement production. In this work, biochar is added as micro-nano particles in different cementitious composites, i.e. cement pastes and mortars, as a function of filler or partial substitute of cement. The main mechanical properties of biochar-based materials are then investigated to determine the optimal percentage of biochar addition

Mechanical characterization of different biochar-based cement composites

Abstract The attention on the use of raw materials, the energy consumption as well as carbon dioxide production of cement factories are boosting the experimentation on innovative and sustainable materials in concrete technology. In recent years, biochar has become an emblematic material with a thousand facets. Mainly investigated up to now as amending in the agricultural field, biochar can be explored as a building material due to its innumerable properties. Indeed, several applications have been studied to use it as a filler to modify the nanogranular nature of the cement matrix, or as a substitute for clinker, aggregates and clay, reducing the carbon footprint and the emissions of greenhouse gases linked to the production processes of cementitious materials. In this paper, nano/micro-particles of biochar, the solid by-product from the gasification process of biomass derived from wood waste, has been used in different cement composites aiming at determining the optimal percentage of addition while trying to guarantee an improvement of mechanical properties. The results showed that an optimized percentage of biochar nano/micro-particles can increase the strength and toughness of the composites

Internal force distribution in RC slabs subjected to punching shear

Reinforced concrete (RC) two-way slabs without shear reinforcement are commonly used in many structural systems. This paper investigated the structural behaviour of RC slabs subjected to concentrated loads leading to punching shear failure using shell and continuum nonlinear finite element analysis (NLFEA). Shear force distributions are studied for four types of slabs with different geometry of support, geometry of slab and layout of reinforcement. All factors investigated have been proven to influence the shear force distributions along the control perimeter around the support. Significant shear force redistributions due to cracking and reinforcement yielding have been observed using NLFEA. Reduced control perimeters to be used for simplified approaches accounting for calculated shear force distributions are calculated using both NLFE approaches

Validation of NLFEA of reinforced concrete walls under bidirectional loading

Nonlinear Finite Element Analysis (NLFEA) of the inelastic behaviour of RC walls are often carried out for uni-directional (in-plane) horizontal cyclic loading. In this paper the behaviour of RC walls with different cross-sections (T-shaped and U-shaped) subjected to bi-directional (in-plane and out-of-plane) loading is simulated by means of NLFEA. They are carried out with the software DIANA, using curved shell elements and a total strain crack model for concrete and embedded truss elements adopting Monti-Nuti model for the reinforcement. The aim of this paper is to validate this type of analysis by comparing the obtained results with experimental outcomes of two different RC slen-der walls, a T-shaped wall and a U-shaped wall, tested under quasi-static bidirectional cyclic load. In particular, the fo-cus is on the comparison between different crack models (Fixed and Rotating crack models) and on the calibration of the Monti-Nuti model parameters for steel. NLFEA is found to acceptably simulate both the in-plane and out-of-plane behaviour observed during the experimental tests. The present work is the starting point for future research in which parametric studies on the influence of reinforcement content and detailing will be performed, assessing their influence on the bidirectional response of RC walls and namely on other less known deformation modes such as out-of-plane in-stability

HER2-Displaying M13 Bacteriophages induce Therapeutic Immunity against Breast Cancer

The advent of trastuzumab has significantly improved the prognosis of HER2-positive (HER2+) breast cancer patients; nevertheless, drug resistance limits its clinical benefit. Anti-HER2 active immunotherapy represents an attractive alternative strategy, but effective immunization needs to overcome the patient's immune tolerance against the self-HER2. Phage display technology, taking advantage of phage intrinsic immunogenicity, permits one to generate effective cancer vaccines able to break immune tolerance to self-antigens. In this study, we demonstrate that both preventive and therapeutic vaccination with M13 bacteriophages, displaying the extracellular (EC) and transmembrane (TM) domains of human HER2 or its Δ16HER2 splice variant on their surface (ECTM and Δ16ECTM phages), delayed mammary tumor onset and reduced tumor growth rate and multiplicity in ∆16HER2 transgenic mice, which are tolerant to human ∆16HER2. This antitumor protection correlated with anti-HER2 antibody production. The molecular mechanisms underlying the anticancer effect of vaccine-elicited anti-HER2 antibodies were analyzed in vitro against BT-474 human breast cancer cells, sensitive or resistant to trastuzumab. Immunoglobulins (IgG) purified from immune sera reduced cell viability mainly by impairing ERK phosphorylation and reactivating retinoblastoma protein function in both trastuzumab-sensitive and -resistant BT-474 cells. In conclusion, we demonstrated that phage-based HER2 vaccines impair mammary cancer onset and progression, opening new perspectives for HER2+ breast cancer treatment

Evaluation of the interaction effects in coupled thin walled prestressed concrete roof elements

In this paper roof elements, representative of typical precast reinforced concrete one storey industrial buildings, will be analysed. In particular non linear finite element analyses will be carried out in order to investigate the interaction effects in coupled thin-walled prestressed concrete roof elements. Coupled roof elements are sometimes used to reduce deformations and stresses in lateral elements subjected both to longitudinal and transversal bending moments and to torsional moment due to un-symmetric vertical loads and wind actio