Good evening, my name is Peter Hughes, I am studying Building Surveying at the University of Central Lancashire. My paper submission is taken from my dissertation, an investigation into the use of synthetic macro fibre reinforced concrete.
I am firstly going to discuss the properties and composites of MSF, then I will outline my experiments, and discuss the main findings. Finally I shall briefly show some applications, case studies from my dissertation of MSF.
The essence of my work is to focus on durability.Millions of pounds of public money has been spent and is committed to the future spending of concrete structures. It is vitally important that our money is well spent and the work is of the highest quality, standing the test of time.
The aspect ratio is shown here, actual fibres will be passed around for you to look at.The use of fibres to reinforce a brittle material can be traced back to Egyptian times when straws or horsehair were added to mud bricks.The addition of Polypropylene fibres was first suggested as an admixture to concrete in 1965 for the construction of blast-resistant buildings for the U.S. Corps of Engineers.
Blend of;Polypropylene; tic tac lid, a good resistance to fatiguePolyethylene; supermarket plastic gagsSamples being passed around; Steel fibresCarbon fibresGlass AsbestosSheffield University are researching the addition of used tyres.
Drying shrinkage crackingPrimary cause – Excess shrinkageIf concrete has been allowed to dry in air, is subsequently placed in water it will swell due to absorption of water by the cement paste.Plastic shrinkage crackingPrimary cause - Rapid early dryingContraction caused by loss of water by evaporation from the surface of the concreteFlexural strengthStrength in tension is of interest to unreinforced structures such as dams, earthquake conditions and the revetment units discussed later. These structures are designed on the basis of flexural strength, which involves strength in tension.ToughnessThe purposes of reinforcing concrete with fibres is to increase the tensile strength by delaying the growth of cracks, and to increase toughness; the total energy absorbed prior to total failure.Flexural ToughnessA key parameter that effects the flexural toughness of concrete is the bond strength between the fibres and the matrix (strength and material composition)Impact resistanceImpact strength is of importance in driving concrete piles, its resistance to repeated blows and to absorb energy. The low rebound number in the experiments may be due to the addition of fibres are acting as impulse absorbers, a useful property on coastal structures subject to cyclic impacts. Abrasion resistanceConcrete surfaces are subject to wear, this may be due to attrition by sliding, scraping or percussion.
My experiments were focused on DurabilityCapillary Absorption – calculation of Porosity and sorptivityRebound numberUPVCompressive strengthSEM
Durability is a vital element
In some circumstances the rebound hammer may be valuable for checking the uniformity of concrete, which can be relevant to durability investigations. Variations in compaction, uniformity of the concrete mix and extent of concrete degradation can be detected. The rebound hammer may therefore be useful for identifying areas of a structure where further investigation is needed, using tests that assess durability more directly.
UPV surprisingly lowPulse velocities in concrete enables variations in quality to be assessed, and areas of poorer quality concrete to be identified. The plot of pulse velocity contours gives a clear picture of variations.Voids and cracks can be detected under certain conditions. This is possible because ultrasonic pulses do not travel through air. The ultrasound has to travel around the air filled crack or void so the transit time is longer in cracked concrete than in sound concrete.
The majority of durability problems relating to concrete are initiated when moisture enter the concrete. Concrete with high sorptivityis more susceptible to penetration by potentially aggressive materials than concrete with average or low sorptivity. The capillary absorption test is therefore of greatsignificance in assessing durability. Generally, concrete of a low water absorption will afford better protection to reinforcement within it, than concrete of high water absorption.
Rebound suggests the MSF may be acting as impulse absorbers
Case studiesBlackpool’s Central Area Coast Protection SchemeMacro Synthetic Fibres have been used to great success at Blackpool’s. It is a prime example of where engineering excellence has been combined with innovative construction products. My paper highlights the advantages and disadvantages of this relatively new product, on site. It focus’s on the revetment units, discussing the challenges faced by the contractor, and gives an insight to the aspirations of the client.
Aci Presentation Peter Hugheslarry
Macro synthetic fibre reinforced Concrete<br />Peter Hughes<br />BSc Building Surveying<br />University of Central Lancashire<br />2008<br />
Properties of Macro synthetic fibres and their composites<br />Outline experimental programme and discussion of results and conclusions<br />Applications<br />Agenda<br />
Local and central Government have committed £800 million in 2010<br />Our vision of the future of concrete should be on its longevity<br />Concrete can perform even under very severe conditions<br />DURABILITY<br />Background<br />
Polypropylene<br />Polypropylene is durable, stiffer than some other plastics, good resistance to fatigue, so that most plastic hinges, such as those on flip-top bottles, are made from this material.<br />Polyethylene<br />The first proposed application was in submarine telecommunication cables. One of the advantages of polyethylene fibre is that it can be produced with a relatively high modulus of elasticity.<br />Fibre Properties<br />
Positive effect on drying shrinkage cracking<br />Positive effect on plastic shrinkage cracking<br />Improves residual flexural strength in excess of 30%<br />Increased toughness, impact and abrasion resistance<br />Some MSF may be used as secondary reinforcement<br />Eliminating steel fabric removes the risk of chloride induced corrosion of reinforcement in marine applications.<br />Benefits<br />
The durability of concrete is one of the most important properties and the focus of attention in my paper. <br />The essence of my work was to discover the effects of adding the synthetic macro fibres and there effect on durability. <br />Durability<br />
Durability of concrete largely depends on the ease with which fluids, both liquids and gases, can enter into, and move through, the concrete.<br />Cracks must be avoided or controlled and minimized because they impair the durability and structural integrity.<br />Permeability<br />
Sorptivity results suggest that the near-surface concrete was far more resistant to fluid ingress in the MSF mix than in the corresponding reference mixes. <br />The impermeability of the MSF demonstrated in the experiment, indicates good resistance to infiltration of solutions. This being an important property to achieve, especially in coastal structures when trying to limit chloride ingress.<br />Summary of main findings<br />
The rebound values for the MSF mix of a mean 30, are surprisingly low for a C40/50 mix. <br />The conversion curve on the hammer and Bungey imply a rebound number in the region of 30 indicates around 30MPa. <br />The compression test gives 50Mpa for the MSF at 56 days suggesting a r number of 40+, yet the number remains constant. This may be a result from the fact that the MSF are acting as impulse absorbers. <br />
UPV tests were most favourable in the OPC design mix. The MSF showed a much lower value. This may be due to the fibre content (dosages of 3.5kg/m3) and its effect on the pulse path being distracted in the sample.<br />
Concrete durability is significantly affected by its permeability, and the penetration of the aggressive liquids, frost action, and steel corrosion are all influenced by the concrete’s permeability. These problems have been decreased by reducing the permeability of the concrete sample. <br />This research presents the development and evaluation of MSF, and their favourable effect on the durability of concrete.<br />
Due to its high residual strength, it is the first synthetic additive truly capable of replacing its steel counterparts in terms of increasing the impact and fatigue qualities of concrete. <br />From Sulphate attack, Freeze/thaw damage, to salt crystallization, salt scaling, abrasion and marine growth, these chemical and physical predators will test the sea walls and concrete structures of our country to their limits. <br />