A calculation model (the Fictitious Crack Model), based on fracture mechanics and the finite element method, 1s presented. In the model the fracture zone in front of a crack is represented by a fictitious crack that 1s able to transfer stress. The stress transferring capability of the fictitious crack normally decreases when the crack width increases. The applicability of linear elastic fracture mechanics to concrete and similar materials is analysed by use of the Fictitious Crack Model. It" Is found that linear elastic fracture mechanics 1s too dependent on, among other things, specimen dimensions to be useful as a fracture approach, unless the dimensions, for concrete structures, are in order of meters. The usefulness of the J-integral, the COD-approach and the R-curve analysis is also found to be very limited where cementitious materials are concerned. The complete tensile stress-strain curve is introduced as a fracture mechanical parameter. The curve can be approximatively determined if the tensile strength, the Young's modius and the fracture energy are known. Su1table~lest methods Tor determining" TRise~~/'Voerties are presented and test results are reported for a number of concrete qua! » a. A new tyr * very stiff tensile testing machine Is presented by which it is possible to carry r . itable tensile tests on concrete. The complete tensile stress-strain curves h •«• feen determined for a number of concrete qualities. The thesi' overs a complete system for analysing crack propagation in concrete as it Include* -ealistic material model, a functional calculation model and methods for determiv" «/ the material properties necessary for the calculations. Therefore this work oi r t to be of use as a base for further studies of the fracture process of concrete < i similar materials.

Crack growth and development of fracture zones in plain concrete and similar materials

On energy-based coupled elastoplastic damage theories: Constitutive modeling and computational aspects

The nominal tensile strength of concrete structures is constant for relatively large sizes, whereas it decreases with the size for relatively small sizes. When, as usually occurs, the experimental investigation does not exceed one order of magnitude in the scale range, a unique tangential slope in the bilogarithmic strength versus size diagram is found. On the other hand, when the scale range extends over more than one order of magnitude, a continuous transition from slope −1/2 to zero slope may appear. This means that for smaller scales a self-similar distribution of Griffith cracks is prevalent, whereas for larger scales the disorder is not visible, the size of the defects and heterogeneities being limited. In practice there may be a dimensional transition from disorder to order. The assumption of multifractality for the damaged material microstructure represents the basis for the so-called multifractal scaling law. This is a best-fit method that imposes the concavity of the bilogarithmic curve upwards, in contrast to the size effect law of Bažant. The relevant results in the literature for ranges in scale extending over more than one order of magnitude are analysed.

Size effects on nominal tensile strength of concrete structures: multifractality of material ligaments and dimensional transition from order to disorder

Research is needed to clarify the interaction between the degree of corrosion, the corrosion crack width, and the load carrying capacity in the presence of a sustained load in reinforced concrete (RC) beams having well-anchored steel reinforcement. This article reports on a study that investigated the combined effect of corrosion and sustained loads on the structural performance of nine RC beams (each measuring 152 x 254 x 3200 mm). One beam was tested as a virgin while eight beams were exposed to accelerated corrosion for up to 310 days using an impressed current technique. Four beams were corroded under a sustained load that corresponded to approximately 60% of the yield load of the virgin beam. The four remaining beams were kept unloaded during the corrosion exposure. Test results showed that the presence of a sustained load and associated flexural cracks during corrosion exposure significantly reduced the time to corrosion cracking and slightly increased the corrosion crack width. The presence of flexural cracks during corrosion exposure initially increased the steel mass loss rate and, consequently, the reduction in the beam strength. As time progressed, no correlation between the reduction in the beam strength and the presence of flexural cracks was observed.

Long-Term Performance of Corrosion-Damaged Reinforced Concrete Beams

Corrosion in reinforced concrete: processes and mechanisms Monitoring of corrosion in reinforced concrete structures Numerical modelling of corrosion in concrete structures Influence of concrete composition Stainless steel reinforcement in concrete structures Surface treatment and coatings for corrosion protection Corrosion inhibitors for reinforced concrete Electrochemical techniques for corrosion protection and maintenance.

Corrosion in reinforced concrete structures

Corrosion of metals in concrete is a continually growing, multibillion-dollar problem, affecting construction, transportation, and many other types of infrastructure worldwide. The influence of corrosion on bond between the reinforcing steel and concrete was studied using a preliminary series of tests on 14 tension specimens, each 100 mm in diameter and 1 m long, and reinforced with one No. 20 bar. The specimens were subjected to accelerated corrosion by immersion in a 5% NaCl solution and subjected to a voltage of 5 v. The relative bond effectiveness of the embedded bars at different stages of corrosion was determined based on the details of the transverse and longitudinal splitting cracks. The bond strength was observed to decrease rapidly with an increase in the corrosion level, dropping from a 9% decrease in the average bond stress for a steel weight loss of 4% to a bond stress decrease of 92% for a weight loss of 17.5%. The latter represented a case of severe corrosion, involving deterioration of the bar ribs.

Corrosion Influence on Bond between Steel and Concrete

The paper reviews current research on the effect of specimen size on compressive, indirect tensile and flexural tensile strengths, the stress-strain characteristics, and related quantities. The measured compressive and tensile strengths were observed to increase with a decrease in specimen size in all investigations. The nondimensional stress-strain curves in compression tests were noted to be homologous for prototype and model concretes. A higher tensile-compressive strength ratio is observed in smaller specimens. The effects of duration and conditions of curing compactions, shape of specimen, and other factors are reported. Techniques are suggested to select the cylinder size to evaluate the concrete compressive strength in a model specimen. To assist with the determination of size effects and standardization, the ACI Committee 444 on Models of Concrete Structures has recommended that model investigations should include compression tests on 2-in.x4-in. (50-mmx100-mm) cylinders along with any other cylinder sizes used.

Size Effect in Model Concretes

Properties of microfine cement grouts at 4 °C, 10 °C and 20 °C

Biodeterioration of concrete sewers is a common problem that results in concrete disintegration and significant damage. Two stages are normally identifiable in the process: an initiation stage, during which the concrete pore water pH is reduced from an initial value of over 12 to a value of about 9 by ingress of hydrogen sulfide gas and carbon dioxide (carbonation) and subsequent reaction with the hydrated cement paste; and a second stage, active biodeterioration, during which microorganisms excrete sulfuric acid that attacks the hydrated cement paste (HCP). Various national codes and standards provide some guidance to mitigate this problem. Sulfur-oxidizing microorganisms growing on the sewer walls have been isolated as the main culprit, but other phenomena come into play before biodeterioration occurs. Steady-state biodeterioration rates of 3  mm/year have been proposed in the literature. A detailed literature review was conducted to evaluate the various aspects of concrete biodeterioration and determin...

Biodeterioration of Concrete Sewer Pipes: State of the Art and Research Needs

Facades, mounted as non-structural elements on the exterior of buildings, contribute to their aesthetics and technical performance, including protection of the building interior from any exterior aggressive environment Unfortunately, design and detailing of facades have received much less attention than the building structure itself Serious incidents of facade failures, including several fatal ones, have occurred all over the world This paper reports the results of a research program aimed at examining the performance and reliability of building facades, considering the various safety-related issues associated with risks involved in design, construction, maintenance, repair, and overall performance of these facades over their entire service life, along with the various failure modes Appropriate strategies are recommended to minimize these risks through improved life-cycle design and construction, and regular inspection and maintenance programs

Saeed Mirza

Papers

Corrosion Influence on Bond between Steel and Concrete

Size Effect in Model Concretes

Properties of microfine cement grouts at 4 °C, 10 °C and 20 °C

Biodeterioration of Concrete Sewer Pipes: State of the Art and Research Needs

Service Life Safety and Reliability of Building Facades