Advances In Concrete Technology

AUTHOR –

COLLEGE OF ENGINEERING PUNE

Abstract Numerous advances in all areas of concrete technology including materials, mixture proportioning, recycling, structural design, durability requirements, testing and specifications have been made. Throughout the world some progress has been made in utilizing these innovations but largely these remain outside routine practice. The use of waste materials in construction is an issue of great importance in this century. Utilization of waste glass and rubber particles in concrete addresses this issue. The combination of waste glass with portland cement or with activated fly ash offers an economically viable technology for high-value utilization of the industrial wastes.

1. Introduction Developing and maintaining world’s infrastructure to meet the future needs of industrialized and developing countries is necessary to economically grow and improve the quality of life. The quality and performance of concrete plays a key role for most of 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. Initial and life-cycle costs play a major role in today’s infrastructure development. 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 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 international research and educational programs is needed.

2. Advances in Concrete Technology Numerous advances in all areas of concrete technology including materials, mixture proportioning, recycling, structural design, durability requirements, testing and specifications have been made. Innovative contracting mechanisms have been considered, explored and tried. Some progress has been made in utilizing some of these technology innovations, but largely these remain outside routine practice. The following sections describe some of the innovations. 2.1. Concrete materials The development of chemical admixtures has revolutionized concrete technology in the last fifty years. The use of air entraining admixtures, accelerators, retarders, water reducers and corrosion inbitititors are commonly used for bridges and pavements. The use of selfconsolidating concrete is beginning (mostly used for precast elements). Shrinkage reducing admixtures are rarely used for bridges and pavements. Supplementary cementitious materials e.g. fly ash, ground granulated blast furnace slag (GGBFS) and silica fume are routinely used. 2.2. Use of recycled materials in concrete The use of recycled materials generated from transportation, industrial, municipal and mining processes in transportation facilities is a issue of great importance. Recycled concrete aggregates and slag aggregates are being used where appropriate. As the useable sources for natural aggregates for concrete are depleted utilization of these products will increase. Utilization of fly ash and GGBFS in concrete addresses his issue in addition to improving concrete properties. The replacement of Portland cement by fly ash or GGBFS reduces the volumes of cement utilized which is a major benefit since the cement manufacture is a significant source of carbon dioxide emissions worldwide. Silica fume is a comparatively expensive product and it is added in smaller quantities in concrete mixture rather than as a cement replacement. 2.3. Concrete mixture proportioning Continuous gradation and consideration of workability during laboratory testing are slowly gaining acceptance in practice. The utilization of laboratory as well as fullscale trial batches are used on major projects.

2.4. Concrete mechanical properties Higher strength concrete for bridges are commonly used for columns and beams. Higher strength concrete usually provide higher abrasion resistance and where appropriate this is considered in the bridge deck and pavement designs. 2.5. Concrete durability properties Concrete durability requirements are specified on most major bridge and pavement projects. Typically the requirements are based on “Rapid Chloride Permeability Test.” This is a surrogate procedure which measures flow of electrical current. The lack of better laboratory and field tests has hindered progress in this area. 2.6. Concrete tests The utilization of advanced test procedures e.g. various shrinkage tests, air-void analyzer and non-destructive tests have become widespread. The non-destructive tests including maturity test are gaining wider acceptability. Workability test for stiff concrete mixes is being evaluated by several organizations. 2.7. Concrete construction control In-situ concrete testing, effective curing practices and utilization of computer software to monitor concrete strength development as well as minimizing cracking potential are used on major transportation projects. 2.8. Specifications Performance related specifications rather than prescriptive specifications for concrete have been developed but not widely used. The use of incentive/disincentive clauses in specifications tend to improve concrete quality.

3. Glascrete: Portland Cement Concrete with Waste Glass as Aggregates

There are some advantages for using mixed color glass aggregate in concrete, especially for some architectural applications. However, being a reactive material, when glass aggregates are added into portland cement concrete, they inevitably result in a long-term durability problem, called alkali-silica reaction (ASR). The product of ASR is called ASR gel, which swells with the absorption of moisture. Sometimes the generated pressure due to ASR gel is sufficient to induce the development and propagation of fractures in concrete. Therefore, the major problem that we need to solve for utilization of glass aggregate in portland cement concrete is how to reduce the long-term damage of concrete due to ASR expansion. There are several approaches that can effectively control the expansion of ASR due to glass aggregate, in addition to the conventional approaches used to minimize ASR expansion of regular portland cement concrete, such as using silica fume and various additives. Firstly, the particle size of glass aggregate is found to have a major influence on ASR expansion. Since the ASR reaction is clearly a surface-area dependent phenomenon, one would expect the ASR associated expansion to increase monotonically with aggregate fineness. However, there exists a size of the aggregate at which the maximum expansion occurs. This is called "pessimum" size. Types of glass also have a significant effect on the ASR expansion. Various types of glass aggregate were tested including soda-lime glass (used in most beverage containers), Pyrex glass, and fused silica. The maximum expansions of mortar bars made with different glass aggregate types differ by almost one order of magnitude. Window glass, plate glass, and windshield glass were found to cause negligible ASR expansion in the ASTM C1260 test. Colors of glass are also important for ASR expansion. Clear glass (the most common kind in waste glass) was found to be most reactive, followed by amber (brown) glass. Green glass did not cause any expansion. Depending on the size of glass particle, green glass of fine particles can reduce the expansion. This implies that finely ground green glass has the potential for an inexpensive ASR suppressant. The green color comes from added Cr2O3 in the glass. However, when chromium oxide is added directly into the concrete mix, the ASR expansion of the concrete is not reduced. So, the ASR suppressing mechanisms of Cr2O3 in green glass needs to be further studied.

4. Rubber Modified Concrete (RMC) The advantages of the rubber modified concrete (RMC) (1) The toughness and ductility of RMC are usually higher than that of regular concrete, which makes it suitable for many applications; (2) The density of RMC is lower than the density of regular concrete; and (3) Comparing with other recycling methods, such as using waste tires as fuel in cement plants, RMC makes a fully use of the high energy absorption feature of the rubber particles. The disadvantages of RMC are – (1) the strength of RMC is usually lower than the strength of regular concrete; and (2) The durability of RMC is not well understood.

Low water-cement ratio significantly increases the strength of rubber-modified mortars (RMM). An 8% silica fume pre-treatment on the surface of rubber particles can improve properties of RMM. On the other hand, directly using silica fume to replace equal amount (weight) of cement in concrete mix has the same effect. In general, the bond between rubber particles and concrete can be enhanced by increasing electrostatic interactions and/or facilitating chemical bonding. Rubber particles were pretreated by coupling agents, and the method was found to be very effective to improve mechanical properties of the RMC. Three coupling agents: PAAM, PVA and silane were tested. Although PAAM is quite effective to improve the interface strength between rubber particles and cement matrix, it has adverse effect on the workability of the RMC when the rubber content is above 10% of total aggregate by volume. Both PVA and silane are very effective in improving the compressive strength of the RMC. There is no adverse effect on workability of the RMC. PVA is more effective than silane for improving the compressive strength of the RMC. The overall results show that using proper coupling agents to treat the surface of rubber particles is a promising technique, which produces a high performance material suitable for many engineering applications.

Alkali slag environmental concrete: Alkali-slag concrete, is made from slag powder and alkali component as main constituents of cementitious material. The slag powder may be one or a mix of the following:

blast furnace slag, phosphorous slag, titanium-containing slag, manganese slag, basic cupola furnace slag, aqueous slag from power plant, nickel slag, silica aluminate. The alkali component as an activator is a compound from the elements of first group in the periodic table, so such material is also called as alkali activated cementitious material or cement. The common activators are NaOH, Na2SO4, water glass, Na2CO3, K2CO3, KOH, K2SO4 or a little amount of cement clinker and complex alkali component; therefore, its activity is more than that of compound from the elements of second group as commonly used in traditional cementitious material. The ions with strong ionic force formed during dissociation of alkali metal compound, promote the disintegration of slag powder and hydration of the ions, and then, such ions take part in the structure formation of cement paste, so the cement has properties of rapid hardening and early strength gain. For such type of concrete there is less Ca(OH) 2 and high alkali hydrates in hydration products of cement, in case of high Al/Si ratio, there will be some mineral of zeolite type resulting in its high resistance to corrosion. Due to perfect pore structure, small total pore volume, proper distribution of pore diameters, dense structure and good bond of interface between cement and aggregate, the special concrete and concrete with the strength of 20-120 MPa can be obtained. The concrete mix has a good workability with slump of 0-22 cm without water reducing agents. The concrete has a high hardening rate with low heat of hydration, consisting of only 1/2 to 1/3 of that for OPC; its impermeability is 1.0-4.0 MPa; the frost resistance reached 3001000 cycles. There is strong protection of reinforcement with excellent corrosion resistance. It can be used for various building elements and monolithic concrete. Structural tests on concrete elements show that their deformation, bearing capacity and cracking resistance conform to the requirements of the China’s standard. For preparing the cementitious material of JK concrete, only the grinding is required with no calcinations. As for the concrete aggregate, the aggregate with large content of mud or fine particles, heavy loam, sea sand, super fine sand, machined sand etc can be used. It is a low cost, energy saving, low resource consumption material, which can promote the recycling of the waste and make an environmental concrete with clean production of cement, environment friendly and in good coordination with the environment. This concrete prepared from pozzolanic slag activated by alkali has excellent mechanical properties and durability, turning the slag into a resource. During cement production, it can lower the environmental load and increase the utilization rate of the slag due to low energy consumption without emission of CO2 and using the mixed slag. During

concrete production, the aggregate with high content of silt and powders can be used as well as sea sand and powder sand, so the environmental characteristics is quite good and can become a new environmental material coordinated with the environment and capable of sustainable development.

Waste Sludge of Smelting Lead and Zinc to Sinter Cement Clinker: For environmental protection, the limitation of waste production and the use of waste materials have aroused worldwide concerns and initiatives. The heavy metal zinc (Zn) and lead (Pb) industries occupy the 4th and 5th position in the world’s metal industries, respectively. According to the manufacturing processes of lead and zinc, the amount of sludge of smelting lead and zinc is almost equal to the product of lead and zinc. More and more sludge of smelting lead and zinc are being produced with the development of zinc and lead industries. Tons of waste sludge for Zn and Pb heavy metal is generated every year. The chemical components of waste sludge of smelting lead and zinc contain mainly SiO2, Fe2O3, CaO, MgO, Al2O3, S, and C. The sludge can be used as a raw material for production of cement clinker. The proportioning optimization can be done to such an extent that the waste sludge of smelting lead and zinc is successfully used for replacing 50% siliceous materials and 100% ferrous materials to sinter cement clinker. Using the waste sludge of smelting lead and zinc to fire cement clinkers can improve the fluidity of raw meal slurry and the burnability of raw meal and promote the strength and performance of the cement.

Barriers in Applications of New Concrete Technology

In order to improve the durability of concrete buildings, bridges, pavements and other structures, not only must the technology or state of the knowledge be advanced, but in addition, that knowledge must of transferred to those doing the work, so that the advancement becomes state of the practice. This “technology transfer” or implementation of the results of research into routine use in concrete mixtures, structural design and construction practices is a challenge that has often lagged considerably behind the actual technical advancements. Research projects need to be developed and conducted with implementation of the results in mind. It is of vital importance to involve the practitioners and users of the research projects in

all the activities from formulation of research ideas and plans through product development, delivery and deployment. This involvement and resultant buy-in from the future users of the technology from the time of research project initiation leads to quicker technology transfer and implementation. Once the research has been completed, a number of possible implementation mechanisms need to be considered in order to select the right approach for successful transfer of the technology to the practitioner. The best approach will depend on the form of the research results. The processes used to bring techniques for improvement in concrete performance and durability through research to practice were discussed in previous sections. Innovation cycle begins and ends with user involvement. Other barriers in the successful implementation of new concrete technologies are as follows: 

No perceived need on the part of the intended user.

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Inadequate Research and Development

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No Champion

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Too complex

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Poor economics

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Institutional opposition

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Lack of persistence

Conclusions and Recommendations •

Significant advances have been made in concrete technology during the last fifty years.

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Many of the innovations have been incorporated in the routine practice.

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Some of the successful examples are discussed in this paper.

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Major barriers in application of new concrete technology remain.

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Technology transfer is not easy.

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In order to speed implementation, research project objectives and scope should fully consider the potential end-use of the research results.

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Practitioner’s input into the formation and conduct of research project is critical to the transition to practice.

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User participation from the early research project stage results in quicker product implementation in routine concrete design and construction practice. The practitioners become “technology champions” through early and continuous involvement in the project.

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Researchers, implementers, and users must be a cohesive team in order to convince others to try new technology.

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Multiple strategies including information dissemination, training workshops, field demonstration projects, hands-on training, equipment loan programs, technical support and educational courses should be considered for research product implementation.

• Adult education and marketing techniques play a major role in technology implementation. This is particularly true for civil engineering design and construction technologies. •

Delivery and full implementation is a long-term process and may require several years of effort. The researchers and implementation team need to continue to be involved in the technology transfer efforts with enthusiasm and confidence for a sustained period.