Yes / The shrinkage force exerted by restrained shape memory polymers can potentially be used to close cracks in structural concrete. This paper describes the physical processing and experimental work undertaken to develop high shrinkage die-drawn Polyethylene Terephthalate (PET) shape memory polymer tendons for use within a crack closure system. The extrusion and die-drawing procedure used to manufacture a series of PET tendon samples is described. The results from a set of restrained shrinkage tests, undertaken at differing activation temperatures, are also presented along with the mechanical properties of the most promising samples. The stress developed within the tendons is found to be related to the activation temperature, the cross-sectional area and to the draw rate used during manufacture. Comparisons with commercially-available PET strip samples used in previous research are made, demonstrating an increase in restrained shrinkage stress by a factor of two for manufactured PET filament samples. / Thanks must go to the EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and to Costain Group PLC. for their industrial sponsorship of the project and author.

No description available.

During the late 70's and early 80's, several precast deck panel bridges were constructed in Florida. These utilize prestressed precast panels as stay-in-place forms and are designed to act compositely with a cast-in-place deck which is poured subsequently. Such bridges offer advantages of quicker construction and lower costs. However, several such bridges built in Florida developed extensive cracking and spalling. Following localized failures, the Florida Department of Transportation has decided to replace all 127 precast panel deck bridges in Districts 1 and 7. Since deck replacement is contingent on funding, it is necessary to develop a rational procedure to decide the order in which they are replaced. This requires a better understanding of the deterioration process and failure mechanism in such bridge decks. The methodology used in this study was to first analyze in detail 5 cases of sudden localized deck failures to identify the causes of the failures and any common factors in the failed bridges. Also, forensic studies were conducted on eight bridges scheduled for deck replacements during 2003 and 2004. In these studies it was possible to investigate in detail the condition of the deck at different stages of deterioration. Based on the information collected, a deck failure model was developed.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) in concrete is a well-known problem and usually occurs within the first few hours after the concrete has been cast. It is caused by a rapid loss of water from the concrete, either from the surface through evaporation or through absorption by dry subgrade or formwork in contact with the concrete and results in an overall reduction in concrete volume. If this volume reduction or shrinkage is restrained, plastic shrinkage cracks can occur. Plastic shrinkage cracks create an unsightly appearance on the concrete surface which reduces the quality of the concrete structure. These cracks also develop weak points in the concrete which can be widened and deepened later on by drying shrinkage and thermal movement. As a result harmful substances may enter the cracks causing accelerated concrete deterioration. These cracks may also expose the steel reinforcement causing it to corrode more aggressively. Consequently, the aesthetic value, serviceability, durability and overall performance of the concrete will be reduced. Therefore it is important to consider methods of limiting PSC. One of these methods is the addition of low volumes of polymeric fibres to concrete to reduce PSC. However, the application of this low volume fibre reinforced concrete (LV-FRC) is not clearly understood since there is a lack of knowledge and guidance available for the use of LV-FRC. The objective of this study is to gain a full understanding of PSC behaviour in conventional concrete and LV-FRC by investigating the effects of evaporation and bleeding as well as the effect of various fibre properties on PSC. The following significant findings were attained: A basis for a crack prediction model in conventional concrete was developed using the average differences in cumulative evaporation and cumulative bleeding to create a crack prediction value (CPV). This preliminary model showed that there exists a certain CPV range (-0.2 to 0.4 kg/m2 for this study) where a slight decrease in the CPV results in a significant PSC reduction. It also showed that if the CPV falls outside this range, varying the bleeding or evaporation conditions will have very little effect on the PSC. A study on the fibre properties in LV-FRC showed that there exist certain limits to the fibre volume, length and diameter where a further increase or decrease in value will have no or little effect on reducing PSC. It also showed that the effect of the fibres depend on the level of severity of PSC. The knowledge gained from this investigation can serve as a basis for the design of a model that can predict the risk of PSC in conventional concrete and specify preventative measures needed to reduce this risk. It also provides information that can be used to develop guidelines for the effective use of LV-FRC. / AFRIKAANSE OPSOMMING: Plastiese krimp krake (PKK) in beton is `n bekende probleem en vorm gewoonlik binne die eerste paar uur nadat die beton gegiet is. Dit word veroorsaak deur die vinnige waterverlies vanuit die beton, óf deur verdamping vanaf die beton oppervalk óf deur absorpsie van `n droeë grondlaag of bekisting wat in kontak is met die beton. Dit veroorsaak `n algehele vermindering in beton volume. As hierdie krimping van die beton beperk word, kan plastiese krimp krake ontstaan. PKK skep 'n onooglike voorkoms van die beton oppervlakte en verlaag die kwaliteit van die beton struktuur. Hierdie krake tree ook op as swak plekke in die beton wat later kan verbreed of verdiep deur droogkrimping en termiese beweging. Gevolglik kan skadelike stowwe vanuit die omgewing die krake binnedring wat lei tot versnelde agteruitgang van die beton. Hierdie krake kan ook die staalbewapening ontbloot wat veroorsaak dat dit vinniger roes. Gevolglik verminder die estetiese waarde, diensbaarheid, duursaamheid en algehele prestasie van die beton. Daarom is dit belangrik om metodes te ondersoek vir die beperking van PKK. Een van hierdie metodes is die byvoeging van lae volumes polimeer vesels tot beton om PKK te verminder. Die toepassing van hierdie lae volume - vesel versterkte beton (LV-VVB) word egter nog nie volledig verstaan nie as gevolg van 'n algemene gebrek aan kennis en riglyne vir die gebruik van die LV-VVB. Die doel van hierdie studie is om 'n volledige begrip van PKK gedrag in normale beton asook LV-VVB te kry. Dit word behaal deur die effek van verdamping en bloei op PKK sowel as die effek van verskillende vesel eienskappe op PKK te ondersoek. Die volgende noemenswaardige bevindinge is bekry. • Die basis van 'n kraak voorspellingsmodel vir gewone beton is ontwikkel deur gebruik te maak van die gemiddelde verskil tussen die kumulatiewe verdamping en die kumulatiewe bloei om 'n kraak voorspellingswaarde (KVW) te vorm. Hierdie voorlopige model toon dat daar `n sekere KVW interval ontstaan (-0,2 tot 0,4 kg/m2 vir hierdie studie) waar slegs 'n effense vermindering in die KVW 'n geweldige vermindering in die PKK tot gevolg het. Dit dui ook aan dat, indien die KVW buite hierdie interval val, ʼn verandering in die bloei of verdamping toestande `n baie klein invloed op die PKK het. 'n Studie oor die vesel eienskappe in LV-VVB het gewys dat daar sekere grense is aan die vesel volume, lengte en deursnee waardes, waar 'n verdere toename of afname in waarde min of geen effek het op die vermindering van PKK nie. Dit wys ook dat die effek van die vesels grotendeels afhanklik is van die risiko vlak vir PKK. Die kennis wat uit hierdie ondersoek opgedoen is, kan dien as 'n basis vir die ontwerp van 'n model wat die risiko van PKK in gewone beton kan voorspel en daarvolgens besluit op 'n voorkomingsmaatsreël om hierdie risiko te verminder. Dit bied ook inligting wat gebruik kan word om riglyne te ontwikkel vir die effektiewe gebruik van LV-VVB.

Concrete structures are in general expected to be subjected to cracking during its service life. This is the reason why concrete is reinforced, where the reinforcement is only activated after cracks occur. However, cracks may be a concern in large concrete structures, such as dams, since it may result in reduced service life. The underlying mechanisms behind crack formations are well known at present day. On the other hand, information concerning the crack condition over time and its influence on the structure is limited, such as the influence of water pressure within the cracks. The aim of this project is to study crack propagation influenced by water pressure and to define an experimental test setup that allows for crack propagation due to this load. Numerical analyses have been performed on an initial cracked specimen to study the pressure along the crack propagation. The finite element method has been used as the numerical analysis tool, through the use of the software ABAQUS. The finite element models included in these studies are based on linear or nonlinear material behavior to analyze the behavior during a successively increasing load. The numerical results show that a crack propagates faster if the water is keeping up with the crack extension, i.e. lower water pressure is required to open up a new crack. When the water does not have time to develop within the crack propagation, more pressure is required to open up a new crack. The experimental results show that the connection between the water inlet and the specimen is heavily affected by the bonding material. In addition, concrete quality and crack geometry affects the propagation behavior.

Structural concrete is the most widely used material in the construction of bridges, pave-ments, runways, dams and other infrastructures which are subjected to uctuating loads during its service period. Concrete contains internal aws in the form of micro-cracks as an inherent property. When subjected to fatigue loading, distributed micro-cracks are formed at the sites of pre-existing aws, which subsequently, localize to form a major crack and propagates. The crack growth curve of a structural component when subjected to fatigue loading depicts a sigmoidal pattern. This curve is divided into three distinct regions namely sub-threshold crack propagation (short crack), stable crack propagation (long crack) and unstable crack propagation depending on the crack propagation rate. Most of the fatigue life is spent in the sub-critical stage (small crack) before the for-mation of long cracks. Hence, from the view of estimating the fatigue life, the crack initiation and early crack propagation (short crack stage) phase are the most important and correct concepts need to be developed. Hence, in this work, the behavior of propa-gation and non-propagationof short cracks in concrete when subjected to fatigue loading is addressed. Small non-propagating cracks are usually found at notch roots when the nominal stress range is below certain limits that depend on the notch sensitivity. Analysis is performed on geometrically similar three-point bend beams of three di erent sizes and subjected to fatigue loading in order to determine the important factors that a ect the notch sensitivity and to determine the minimum stress range required for the initiation and propagation of short cracks. A criterion for crack initiation and propagation is proposed based on linear elastic fracture mechanics. Using this criterion, the maximum length of non-propagating crack that can be formed from fatigue loading alone and the minimum stress range required to propagate a crack without arrest are computed. It is observed that the notch sensitivity increases with increase in beam size, decrease in notch-tip aspect ratio and increase in the fatigue limit of the material. Since the probability of formation of a non-propagating crack at a notch tip decreases with increase in notch sensitivity, and since it is desirable not to have a non-propagating crack in experimental investigations, it is essential to design a specimen with higher notch sensitivity. A crack spends a considerable amount of time in the short crack regime. The short cracks are found to propagate at higher rates than the long cracks at the same nominal stress intensity factor which is known as the short crack anomaly. It is important to consider this anomaly in the prediction of the residual life of damaged concrete structures. Hence, in the present work, an analytical model is developed using the principles of dimensional analysis and self-similarity in order to estimate the rate of short crack growth in concrete. The important parameters such as load range, threshold value of stress intensity factor range, modulus of elasticity, tensile strength, fracture energy, stress ratio, crack size and the maximum aggregate size are considered in the development of the short crack growth model. The model is calibrated and validated using the experimental results that are available in the literature. A probabilistic analysis is carried out to determine the sensitivity of each of the di erent parameters that has been considered on the crack growth rate using the coe cient of variation method. It is found that the crack length is the most sensitive parameter to short crack growth rate followed by the load range. A term called `characteristic fatigue life of short crack' is de ned as the number of fatigue cycles that can be applied such that not more than ve percent of the short cracks is expected to proceed to the long crack regime. Furthermore, the fatigue life of a crack spent in the short crack regime is determined through a reliability based study using the Monte Carlo technique. It is found that the smaller sized specimens have larger fatigue life in the short crack regime than the larger specimens.

The aim of this thesis is assessment of existing condition reinforced concrete factory chimney, who has undergone structural and technical survey, under which was found many failures caused of horizontally tension - significant vertical cracks in the chimney stack. The object of this work will also make appropriate proposals rehabilitation of concrete stack by design prestressed cables monostrand in horizontal direction, grouting open cracks and reprofiling surface of chimney stack.

This master thesis gives overview of non-destructive tests of concrete and provides detailed information concerning the acoustic and electromagnetic emission during monitoring of concrete failure. Conducted loading tests of plain concrete specimens are described in the thesis together with the performed numerical simulations of these tests in the software ATENA. The simulation results of concrete failure are analysed in detail and compared with the experimental results recording failure processes with the help of acoustic and electromagnetic emission. The majority of simulation results in software ATENA 3D show good agreement with the recorded data.