We recently made a survey via Linkedin trying to figure out what the main barriers and limitations for a widespread use of UHPC (Ultra-High Performance Concrete) in the industry are. People from many different sectors, such as specialized UHPC companies (33%), the academia (22%), civil engineers (14%), precast sector (11%) or fiber producers (11%) participated. […]
In the third post of “Tensile behaviour of UHPC” we start talking about UHPC…, finally 🙂 Don’t miss the two previous posts dealing with tensile properties of plain concrete and some important properties of it, such as scale-effect and brittleness. In this post we talk about (i) the reason underlying the use of fibres in concrete; (ii) the mechanical response of fibre-reinforced concretes and how it differs from plain concrete; and (iii) we show a typical constitutive behaviour of UHPC. Enjoy it !!
ReSHEALience Project started with the purpose of increasing service life by at least 30% and decreasing maintenance costs by at least 50% of those structures exposed to aggressive environmental conditions, such as chemical attacks or chloride induced corrosion, throghout a thorough research and innovation 4-years project focused on four main areas: (i) improvement of material durability properties; (ii) improvement of design criteria in service life conditions and prediction of structure lifespan; (iii) full scale monitored prototypes to check technical feasibility; and (iv) evaluation of business opportunities to check economical, social and environmental feasibility. We want longer-lasting structures with lower maintenance costs !! We believe concrete is the best choice !! And we want them to be sustainable and competitive !! Does it a lot to ask?
Achieving such ambitious goals will require the joint effort, commitment and determination of 14 different partners (companies, universities and research institutions) for the development and realisation of what we have called: Ultra High Durability Concrete (UHDC). It is not just the development of an hiper-ultra-mega-super concrete, but a lot more than that. So, what does this new concept mean?
Fibres may be considered the most important ingredient in the recipe for UHPC due economical, ductility and durability reasons. ECONOMICAL. An analysis of the raw materials required to produced UHPC shows that approximately 60-80% of the total price is due to fibres in a common UHPC with 2% in volume of steel fibres. This ratio can be much higher if either stainless steel fibres or larger fibre amount is used. DUCTILITY. On the other hand, it is unsafe to design UHPC structures without fibres since a minimum material ductility is required !! Fibres provide that ductility when using properly. DURABILITY. Besides, fibres help control cracking, which also contributes to increase the lifespan of structures. That is why is completely necessary to know some key points about its use. ¿Interested?
In the first post of “Tensile behaviour of UHPC” we defined the uniaxial tensile behaviour of plain concrete using both a stress-strain relationship up to maximum load and a stress-crack opening relationship from this point onwards up to a maximum crack width. We explained that one of the main consequences of the ability of concrete to transfer a “stitched force” between the two planes of a crack according to the distance between them (crack opening) is the fact that strength depends on specimen size, what is commonly called scale-effect. It could have been a minor issue for science if not for the fact that linear elastic theory couldn’t predict that. In this post we are going to explain (i) the concept of equivalent flexural strength; (ii) the nature of the scale-effect phenomenom, (iii) the way we can easily consider the scale-effect by correcting softening stress-strain behaviour according to structure depth and (iv) some notions about brittleness.
Warning 1: We strongly recommend to read post (I) before digging into this one !!
Warning 2: It may be kind of tedious to read if you don’t have basic knowledge on concrete design !!
Let’s get started !!
One of the key features of UHPC is its ability to create multiple microcracks closely spaced to each other under certain conditions. This is the so-called multi-microcracking process that characterises strain-hardening materials, i.e. those materials that are able to hold a constant stress throughout a crack even at high strain values. However, one may consider that multi-microcracking is not a property of UHPC, i.e. a material property, but a property of the structure made with it. It means that even though we have obtained a strain-hardening behaviour in lab conditions using standard specimen and tests methodologies, it is possible that our designed structure behaves as a strain-softening one. Why is that? The answer is found in the fact that development of strain-hardening process in a structure mainly depends on (i) the nature of forces acting on it and (ii) fibre orientation inside the element which may differ a lot depending on element thickness and pouring system. Therefore, even though UHPC shows a strain-hardening behaviour under standard lab conditions, we need to know in which situations we can consider it or not in design. In this post we show a structural application in which consideration of strain-hardening behaviour is not only possible but a also a must to predict its real behaviour. Do you want more info? Keep reading 🙂
As year 2017 is drawing to a close, and for sure, your agenda is full of feasts, family gatherings and wonderful presents, we think it is the right time to take a short break and wish you a Merry Christmas and a happy New Year from all the RDC staff. Let us seize this post to look back over the most important milestones of the year and look forward to what it is yet to come in 2018. Don’t forget to subscribe to our blog !!
High performance in tension is probably the most important feature of UHPC, and fibres are responsible for that. They play a major role in ductility, crack control, durability and strength. As they also represent 60-80% of UHPC cost, it is completely necessary to understand how they work, i.e. tensile response of UHPC. Its knowledge and suitable consideration in design is a must to achieve safe and competitive designs.
With this purpose we start a series of posts dealing with the tensile performance of UHPC. I always like to start with a little bit of background. UHPC tensile behaviour can’t be fully understood without a previous knowledge of the tensile behaviour of plain concrete. Let’s start with it and with some interesting notions you may not know about its response and scale – effect.
Warning: It may be kind of tedious to read if you don’t have basic knowledge on concrete design !!
Our adventure through the Project SELMUS (H2020 | SME Instrument programme) focused on the development, testing and full-scale demonstration of a revolutionary floating platform made of UHPC to boost competitiveness of the mussel culture sector, has been the gateway to RDC participation in another project supported by European Comission inside the Research & Innovation Action (RIA) programme. A total of 14 different partners from different EU locations are involved in this new project entitled “Rethinking coastal defence and Green-Energy Service infrastructures through enhanced-durability high-performance fibre reinforced cement-based materials”. As could not have been otherwise, UHPC has a main role in this project. Do you want to know a little bit more about it? Do you want to follow the continuous project’s progress? Keep reading.
One of the main barriers for an increasingly use of UHPC in concrete precast industry is the difficulty of finding a realiable UHPC mixture at an affordable price. If you want to start producing UHPC elements you have two choices: (i) ask specialised companies, commonly cement companies, to provide you with some of their already developed premixes, or (ii) develop one of your own.
If you have already asked these specialised companies for a high-quality and reliable UHPC supply and you think what they offer to you is far from making your products competitive (which may be the most likely scenario) and you are afraid you can’t do it on your own, in this post you can find some basics you need to follow. Why not give it a try?