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NEW TRENDS IN CONCRETE TECHNOLOGY PDF

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Recent Trends in Concrete Technology - Free download as Word Doc .doc /. docx), PDF File .pdf), Text File .txt) or read online for free. ICCBT Emerging Trends in Concrete Technology and Structural Concrete K. U. Muthu, M. S. Ramaiah Institute of Technology, INDIA ABSTRACT This. Past ten years witnessed a number of advances in new concrete technology. In almost the major part of the concrete industry itself haven't adopted these new .


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Recent Advances and Trends in Concrete Technologies by. John J. Myers, PhD, PE. Associate Professor and Interim Center Director for the Center for. Department of Civil and Environmental Engineering. Northwestern University. “ New Trends in. Concrete Technology”. Friday, March 12, developments, and new innovations in concrete technology. regarding the future and development trend of concrete have been discussed. Although the book.

Changes in global markets, increased customer expectations, and government pressure have all led to innovation becoming a key focus for the construction sector. There is increasing pressure on the construction industry to become more environ-mentally sustainable. As the construction industry is a major energy user as well as contributer to the greenhouse gas emissions and waste levels, the government is pushing hard to the construction sector to come up with more and more innovative technologies in concrete since concrete is the mother constituent of any construction.

The quality and performance of concrete plays a key role for most of the infrastructure including commercial, industrial, residential and military structures, dams, power plants and transportation systems. Concrete is the single largest manufactured material in the world and accounts for more than 6 billion metric tons of materials annually.

The industrialized and developing world is facing the issues related to new construction as well as repair and rehabilitation of existing facilities. Rapid construction and long term durability are requirements on most projects.

There have been number of notable advancements made in concrete technology in the last fifty years. Some of these advances have been incorporated in routine practices.

But, in general, the state-of-practice has lagged far behind the state-of-art.

This is particularly true for public sector projects. There is an increasing concern in most parts of the world that it takes unduly long time for successful concrete research products to be utilized in practice.

Even though some advances have been made in quick implementation of new concrete technology, significant barriers to innovation and implementation remain. Continued coordination of ongoing inter- national research and educational pro-grams is needed. Numerous advances have been made in all areas of concrete technology including materials, mixture proportioning, recycling, structural design, durability requirements, testing and specifications. Throughout the world some progress has been achieved in utilizing these innovations but largely these re-main outside routine practice.

The high performance concrete HPC for transportation structures, e. HPC provides enhanced strength and durability properties and contributes towards long lasting structures and pavements. The constructability can also be enhanced by proper mixture proportioning and testing.

Most HPC mixture include re-cycled materials e. The use of recycled materials in construction is an issue of great importance in this century. The reduction of Portland cement production will reduce carbon dioxide CO2 emissions, reduce energy consumption and reduce the rate of global warming. Utilization of fly ash and GGBFS usually provides cost savings as well as improved concrete properties.

The case histories discussed demonstrate the practical uses of supplementary cementitious materials. The successful utilization of supplementary cementitious materials requires proper mixture pro-portioning, testing, placement and curing. Lack of widespread transfer of developed and available new concrete technology is a major problem in most countries. The past experience has shown that successful technology transfer occurs when there is a pressing national need, champions of technology are created, champion and organizations involved persist, practical demonstrations of technology are conducted to demonstrate benefits, and regulatory requirements are implemented.

The new concrete technology must fulfill a need to be successful. The user starts and ends the techno-logy process. Examples of successful concrete technology transfer efforts are discussed.

Some Emerging Trends and Innovations in Concrete 1. Green Cements 3. Smart Concrete 6. Use of Recycled Tire Rubber in Concrete 7. Smog Eating Concrete 8. Translucent Concrete Low Temp. Concrete Admixture Prepacked Shotcrete Admixture Steel-Free Concrete Bridge Deck Pavemend — Rapid Repair Products Precast Inverted T Beam Conductive Concrete Corrosion Inhibitors for Reinforced Concrete Shrinkage Reducing Admixture for Concrete CKD contains partially calcined materials with some hydraulic and cementitious properties.

It also has high alkali, chloride, and sulfate content, which may cause problems in cement performance. Blended Cements An important concept of concrete technology innovation is blended cements.

It makes use of industry by pro-ducts like fly ash and blast furnace slag, which otherwise would have required land for its disposal. The concept also gives lesser natural lime stone and lesser emission of CO2 to atmosphere.

High Performance Concrete HPC Normal Strength Concrete NSC is heavy and lacks the required work-ability in some large concrete structures, such as high-rise buildings, bridges, and structures under severe exposure conditions.

Recent Trends in Concrete Technology

By increasing concrete strength and performance, the required thickness of concrete members and the cost of concrete structures can both be reduced. In the U. A major demonstration precast concrete bridge is under construction in Texas. HPC can be defined as a concrete made with appropriate materials superplasticizer, retarder, fly ash, blast furnace slag and silica fume combined according to a selected mix design and properly mixed, transported, placed, consolidated, and cured to give excellent performance in some properties of concrete, such as high compressive strength, high density, low permeability and good resistance to certain forms of attack.

Smart Concrete Concrete has been widely used for many years as a composite material for various types of structures.

RECENT TRENDS IN CONCRETE TECHNOLOGY

The designed mix has been used to make a comparative study on the behaviour of cement concrete pavement slabs. Concrete pavement slabs of thickness , and mm of size Xmm were cast and the temperature variations over the depth of the slab were studied and the results are presented.

The study indicates that HVFA concrete with Metakaolin specimen exhibits good resistance to thermal gradients [28]. The measured temperature differential has been used to compare the curling stresses in the slabs using theoretical models proposed by a Bradbury and b Timoshenko model.

It is being recognized that concrete having greater than 55 MPa is termed as high strength concrete. High strength concretes can be modeled as a three phase composite material compared with the conventional concrete, the three phases being i hardened cement paste ii aggregate iii interfacial zone between the hardened cement paste and the aggregates.

These three phases must be optimized, which means that each must be considered explicitly in the design process. For high strength concretes, all the components of the concrete mixtures are pushed to their critical limits in such a way that the strength of all three phases are made higher.

HSC is obtained by improving the compactness of the concrete mix, which increases the strength of paste and interface between the paste and the coarse aggregate. The stress strain behaviour, ultimate strain, strain softening slope, cracking and modulus of elasticity of HSC beams has varied with source and time. ACI defines HSC as concrete made use of normal weight aggregates having compressive strength of 41 MPa or greater and shall not include concrete made using exotic materials or techniques.

Advanced Concrete Technology

The word exotic was included in the definition so that committee would not be concerned with concretes such as polymer impregnated concrete, epoxy concrete or concrete with artificial, normal and heavy weight aggregates. Bertero [31] considers high strength concrete with compressive strength greater than 41 MPa for normal weight concrete and 27 MPa for light weight concrete aggregates. In the recent past, concrete having compressive strength of MPa were produced and termed as ultra high strength.

Typical constructions of Sherbrooke Bridge Quebec in Canada and a foot bridge in Seoul are the typical constructions. It has been observed that the stress strain curve of HSC was steeper compared to that of normal strength concrete. Stress- strain diagram for HSC beams is more linear when compressive strength increases.

A few codes of practices [] incorporated the work of Li [35] and Ibrahim and Mac Gregor [36]. Different codal provisions were also examined for the ultimate flexural strength of HSC beams.. The ultimate moment capacity by various codes of practices do not vary much and it should be noted that all practically designed beams are under reinforced and their flexural strength is governed by the yield force in the steel. Muthu should be mentioned here that the maximum tensile steel ratio increases linearly with grade of concrete [37].

A few investigations were reported on the flexural behaviour of minimum flexural reinforcement []. Many of the codes of practices depend on the Strut and Tie approach or Plasticity approach []. Rangan [48] suggested a variable angle truss model for the practical beams as they do contain only light shear reinforcement.

In recent times, attempts have been made to predict the shear strength of the beams using ANN [].

Bentz [51] gave an approach to predict the shear strength of beams satisfactorily. An investigation has been carried out [52] to study the shear strength of beams. Twelve high strength reinforced concrete beams were tested of grade M and M They ware provided with constant longitudinal reinforcement of 2. The beams were of rectangular sections Xmm and the effective span of mm so that the shear span provided is and mm respectively. The study indicates that though a larger data base is available and few theoretical approaches were developed, there is still further scope for the development of a suitable analytical method.

The slab is treated as a thin plate and the elastic theory of plates has been used. It essentially requires the solution of fourth order differential equation for a given loading and boundary conditions.

The solutions of different shapes of slabs with the prescribed boundary conditions are available in Timoshenko and Kreiger [54], Jaeger [55], Szilard [56] and Ugural [57]. Vladimir Panc [58]. The theory is useful in predicting the elastic behaviour of slabs, but the factor of safety against collapse cannot be assessed. The analysis is quite involved if the slabs are irregular in shape which can be analyzed using yield line analysis.

He found that during testing of the slabs, they failed with different pattern of fractured lines forming the segments of slabs. He proposed the method based on bending moments acting along the yield lines.

The basis is as follows. An increase in the load causes concentration of strain in steel along the lines on moment.

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These lines are called yield lines and they spread into pattern which divides the slab into segments. The elastic deformations are neglected and all the curvatures in the slab are assumed to be concentrated at the yield lines. The energy equation has been used to determine the yield line load based on the assumed mechanism. It is based on upper bound theorem where in the mechanism and equilibrium conditions are satisfied. Though this theory is suitable for the ultimate load analysis of isotopic and orthotropic reinforcement, it is difficult to handle if non uniform or curtailed reinforcement is utilized.

The reinforcement volume becomes uneconomical if the correct mechanism is not assumed properly. It does not indicate the load on edge beams and also the distribution of bending and twisting moments in the interior of the slab away from the yield lines is unknown.

This theory is widely accepted as the ultimate loads of the tested slabs are higher than those predicted by yield line theory. The difference in load estimation is due to the arching action of slabs which is discussed in the subsequent sections. This provides a safe solution because the collapse load may be greater than or equal to the calculated value.

The lower bound solutions are available for simply supported, continuous, one short edge free, rectangular and circular slabs [60]. Hillerborg [61] developed the strip method based on the lower bound approach. The load was assumed to be carried by the bending moments in two perpendicular directions and the torsional moments were neglected in developing the method.

20 EMERGING TRENDS SHAPING THE WORLD OF CONCRETE

This method is simple for slabs with free, simple and fixed boundary conditions as the slab can be divided into simple combinations of cantilever and simple beam strips. This is essentially a design method and economy is achieved by varying the reinforcement in different portion of the slab.

Wood and Armer [62] investigation pointed out that the strip method provides an exact solution if the reinforcement provided matches with the strip moments with an unlimited number of simultaneous modes. Hillerborg [63] further proposed the advanced strip method which includes supports like interior, exterior corner columns and reentrant corners. The moment fields were designed instead of strip loads at the critical locations so that the moments are in bimoment equilibrium with the applied loads.

Subsequently Gurley [65] has presented design methods for slabs by considering them as torsion free grillages. The presence of in plane forces increases the load carrying capacity. The in plane forces develop due to change in geometry. Muthu and there exists compressive and tensile arching action. The compressive arching action is predominant in restrained slabs while the tensile membrane action occur at large deflections in case of simply supported slabs.

Though arching action has been recognized since , the major design codes ACI [66] , BS [67] and Eurocode [68] ignore the effect of arching action in slabs, a few recent design standards recognized the membrane action and included in the specifications of the department of the Environmental Bridge designs [69] and the Highway Bridge Design code [70].

Recent studies of Taylor et al [74] and Alan et al [69] were focused on the arching action of HSC slabs. Though many investigations have been reported on rectangular and skew slabs, the literature pertaining to strength and deformation of circular slabs are very few. Wood [71] analyzed the arching action in isotropic circular slabs.

Desayi and Kulkarni [75] extended the above approach to orthotropic restrained circular slabs. Their method was based on deformation theory. Calladine [76], Janas [77], Morley [78] have applied flow theory for circular slabs with ring beams. Morley [79] tested circular slabs with ring beams. Al Hassani [80] used the deformation theory for the ascending part of the load deflection curve and flow theory for descending portion of the curve.

Braestrup and Morley [81] proposed a modified rigid plastic theory for circular slabs with ring beams.

Recently the author and his associates developed analytical methods including arching action in restrained slab strips [82] partially restrained slab strips [83] and circular slabs with edge restraints [84].

The estimation and control of deflections was found to be essential with the use of high strength concrete and high strength steel, efficient design procedures and lower partial safety factors.

The first method is the control of deflections where in the minimum thickness is specified and if the designers provide a thickness greater than above, it is presumed that the resulting total deflections would be within permissible deflections. The second method is the computation of deflections based on elastic theory.

It is implied that the deflections can be computed to ensure that they do not exceed the specified maximum allowable values. Holding stocks or shares in an organization that may in any way gain or lose financially from the publication of the article, either now or in the future. Holding, or currently applying for, patents relating to the content of the manuscript. Any paper lacking it will not be considered for publication. When informed consent has been obtained, it should be indicated in the published article.

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Bischoff [92] proposed an effective moment of inertia function based on tensioning effect. Silica fume also has a packing effect to further improve the matrix density. Thus, the maintenance cost for concrete structures is much lower than that for steel or wooden structures.

In the recent past, concrete having compressive strength of MPa were produced and termed as ultra high strength. The cover is often various rubber or plastic compounds specified by use of the belt. It is implied that the deflections can be computed to ensure that they do not exceed the specified maximum allowable values.

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