INNOVATIONS IN CONCRETE PAVEMENTS Satander Kumar, Consultant, National Council for Cement and Building Materials, Ballabgarh, Haryana. ABSTRACT Presently, new innovations in concrete pavement are completely changing its design and construction. New-age concrete of compressive strengths more than 200 MPa also has very high tensile strength with or without the inclusion of steel/ synthetic structural fibers. Higher flexural strength requires less thickness of pavement quality concrete. Similar types of concrete mix proportions are referred in IRC: SP: 83-2008 for “Early Opening to Traffic” (EOT) concrete pavements and also for the maintenance. Among other special concrete, Self Consolidating Concrete (SCC) eliminates the need of mechanical consolidation and electrical energy at site and yields required surface finish without segregation and undulation in the insitu or precast concrete slab for rigid pavement. In recent times, SCC is recommended in IRC:SP-62-2014 for construction of low volume concrete pavements for village roads where skilled labour and mechanical/ electrical energy may not be easily accessible. The best use of SCC; is in pre-cast concrete pavement and heavily reinforced concrete structures or where placing of concrete from a single point is only feasible. This technique is being widely used in Japan. Equally, there are many other technologies which are cost effective and environment friendly. Advance equipment like digital/laser thermometer, distansometer, relative humidity meter, wind speed meter, small kits for rapid testing of water, maturity meter, mobile batching plant, mobile crusher for aggregates etc., automatic steel bar cutting and bending machine are being used in India. Portland cement production is so GHG-intensive, that the challenge is to produce concrete pavements with the same quality and strength using less Portland manufactured cement, but more supplementary cementing materials, but greener and cheaper product, with additional benefits to control alkali silica reaction (ASR). Field evaluation technologies viz, pullout test ASTM C-900, Windsor HP Probe test (Bullet test) ASTM C- 803 on hardened concrete etc., are also in use now in addition to core testing/rebound hammer/ultra sonic pulse velocity as per IRC:112. IRC:117-2015 may also be adopted for evaluation of rigid pavement with Falling weight deflectometer (FWD) to check voids between two layers (concrete layer and dry lean concrete/granular layer/subgrade) due to repeated heavy loading and other engineering parameters. The paper thus describes new cost effective innovations for making good quality concrete pavements and their evaluation for the prevailing traffic with saving time and energy.
1. INTRODUCTION Considering history of concrete making and catastrophes, very useful things can be made from concrete and individual designs that can take advantage of the shape and cast ability of concrete. Concrete is the "liquid stone", mankind has been searching for, throughout history. Concrete allows the human mind to design a shape and form the shape with common building materials and then pour the concrete into the form and shape a structural reality. The concrete form and cast system is much more economical and efficient than conventional like stone block pavement/stone set pavement in time and money. 1
Continuing with the history of concrete, liquid chemical and solid mineral admixtures came into existence since 1930s. These items are generally called lignin of lye and a powder product called fly ash/calcined clay. These two products, when in combination or separately, added to concrete, reduced the amount of water (and there by cement also) normally used in the concrete to make it economically workable. In the last 75 years, there have been changes in the makeup of concrete. Some of the changes have been for the good. Concrete now includes mineral admixtures (fly ash, silica fume, powdered reactive granulated blast furnace slag, properly calcined powdered rice husk ash etc.) as per IS: 456 and chemical admixtures (plasticizers, super plasticizers, retarders, air entraining agent etc. as per IS: 9103) including polymeric and steel fibers (IRCSP: 46). Many of these affect the amount of water required to produce a usable concrete. Concrete shall be designed to do the job; and always be cured to gain its full potential in strength and shall be maintained to protect it into the future. The latest new concrete technologies are beginning to gain acceptance in the industry. Some of new concrete technologies are given as under: i) ii) iii) iv) v) vi) vii) viii) ix) x) xi) xii) xiii) xiv) xv)
Recycled concrete pavements, Roller compacted concrete pavements (IRC:68-2005), Ultra high performance concrete pavements (IRC:SP:76-2015), Thin and Ultra Thin white topping and bonded concrete pavement (IRC:SP:76-2015) Bonded concrete pavement (IRC:58-2015) Porous concrete pavements High volume processed fly ash concrete pavements, Fibre reinforced concrete pavements, Continuously reinforced concrete pavements i.e. joint-less rigid pavements IRC:118, No joint sealant concrete pavements as per ACPA Very thin concrete cloth/canvass in the form of roll, Engineered cementitious composites pavements, Micro cement/ micro-crete using nano-particle Geo-polymer concrete pavement, Precast concrete pavement etc,
These innovations have significant advantages and are need based with little or no disadvantages when compared to conventional material in use. After completion of satisfactory trials and field study with these new innovations, codes are usually being drafted/modified/revised after discussion in the respective technical committees of Indian Roads Congress (IRC)/ Bureau of Indian Standard (BIS) for their wider application. 2. RECENT CODES/ GUIDELINES/ SPECIFICATIONS List of latest few National and International Codes on concrete pavement based on satisfactory performance are given in Table 1. 3. BASIC REQUIREMENT OF INNOVATIONS Cement is the most consumed man made product in the world with constantly growing demand. Portland cement production consumes more energy and pollutes world more than any other industries by contributing up to 8% of all greenhouse gases just by itself while keep growing about 5% annually. The main issue is how to control greenhouse emissions (GHG) ? Since Portland cement production is so GHG-intensive, that the challenge is to produce concrete structures with the same quality and strength 2
using less Portland cement, but more supplementary cementing materials to form the same quality, but greener and cheaper product. Production of cement is one of the largest industrial sources of CO2 emissions. In context of, very rare availability of good quality aggregates, the speed and buildability, adequate pre-planning, precasting of elements and the use of appropriate technology in design and construction can make concrete the cheapest and fastest material for constructing durable concrete roads. Table 1: Currently Available National and International Codes on Concrete Code No IRC:SP: 46-2013 IRC:SP:62-2014 FHWA-IF-03-00702 IRC:SP76-2015 IRC: 85 -2014
Title Guidelines for Design and Construction of Fibre Reinforce Concrete Pavement Guidelines for Design and Construction of Cement Concrete Pavements for Low Volume Roads Technical Brief Ultra Thin Whitetopping
Tentative Guidelines for Conventional, Thin and Ultra-Thin White toping Recommended Practice for Accelerated Strength Testing and Evaluation of Concrete for Road and Airfield Pavements IRC:SP-86-2010 Guidelines for Selection, Operation and Maintenance of Paver Finishers IRC:SP-96-2012 Guidelines for Selection, Operation and Maintenance of Concrete Batching and Mixing Plants IRC:SP 113 -2013 Guidelines for Design and Construction of Geo-synthetic Reinforced Embankments on Soft Sub Soils IRC:114-2013 Guidelines for Use of Silica Fume in Rigid Pavement IRC:75-2014 Guidelines for the Design of High Embankments ASTM C457/ Standard Test Method for Microscopically Determination of Parameters of the AirC457M - 2012 Void System in Hardened Concrete ASTM C -900- Standard Test Method for Pullout Strength of Hardened Concrete 2006 ASTM C856-2014 Standard Practice for Petrographic Examination of Hardened Concrete IS: 3812 (part 1) Pulverized fuel ash — Specification part 1 for use as Pozzolana in Cement, Cement :2013 Mortar and Concrete IS: 8112-2013 43 Grade Ordinary Portland Cement Specification IS: 10262-2009 Cement Concrete Mix Design IS: 13311-1999 Non Destructive Testing of Concrete MORTH -2013 SPECIFICATIONS FOR ROAD AND BRIDGE WORKS (Fifth Revision)Published by Indian Roads Congress, NEW DELHI
4. NEW PRODUCTS MADE WITH INDUSTRIAL BY-PRODUCTS AND FIBRES High performance concrete usually contains cement, aggregates, water, chemical admixtures and byproducts and thereby reduces the need to dispose of these materials which are having too much potential energy in them. Some of such materials consist of pozzolana i.e fly ash (waste by-product from powdered coal burning), ground granulated blast furnace slag (waste by-product of steel industry), and silica fume (a waste by-product of ferro-silicon alloy industry). But perhaps the biggest benefit of using some of these is the reduction in the need to use Portland cement for green environment. It is estimated that the production of cement worldwide contributes five to eight percent of global carbon dioxide emissions. 3
4.1 Mineral Admixtures: As per CPWD circular dated 2004, partial use of flyash in concrete is permitted ( i.e replace only 15% cement with 25% dry fly ash in Ordinary Portland Cement based on different specific gravities of each materials). Similarly potentially reactive powdered granulated blast furnace slag (upto 50 % by weight of Portland cement and upto 65% as per IS: 456) is permitted for cost effectiveness as compared to virgin cement for improving the quality of the final concrete particularly in harsh chemical environment. Today’s new types of concrete have live spans measured in the hundreds of years rather than decades. The use of by-products will save hundreds of thousands of acres of land that would have been used for disposal purposes. Many countries including India are exporting fly ash to oil producing countries where soil and aggregates contains harmful salts and number of coal based power plant are very restricted. 4.2 BSI : It is a trade name as per http://www.isnare.com and is a new concrete technology that has a much higher tensile and flexural (bending) strength than standard concrete. It is a fiber-reinforced concrete that is combined with premixed dry components. It is much denser than standard concrete and concrete road built with it will need far less new concrete, perhaps as much as 80% less. The high density BSI concrete gives other properties such as extremely high resistance to corrosion from chemicals. The higher strength of BSI eliminates the need for placement of steel rebar in structural designs 4.3
Ductal: It is another new concrete technology that is denser than BSI. Ductal uses steel or high strength organic fibers to create a concrete that is stronger than BSI. Interestingly, the ancient Romans used horse hair in their concrete to improve its strength. Ductal is being tested for use in earthquake resistant structures, bridges, tunnels, and nuclear containment structures and may be tried in special purpose concrete pavement. In addition, both BSI and Ductal have low maintenance. These are both resistant to salt water and may be tried in reinforced concrete pavement.
4.4
Engineered Cementitious Composites: These are being used for structural application. Limitation of high strength concrete is due to its core issue of brittleness as measured by brittleness number which usually increases as the compressive strength of concrete increases. So there is a need to use cost effective, high ductile cementitious material for such applications. University of Michigan has been working on Engineered Cementitious Composite (ECC) Material which is a mixture of water, cement, sand, special fibres and some common additives. A typical composition employs W/C ratio and sand/cement ratio of 0.5 or lower. Amount of fibres used in it is lesser than used in high performance fibre reinforced concrete. Fracture toughness of ECC (30kJ/m2) is similar to that of the Aluminum alloy and compressive strain capacity is approximately double than that of fibre reinforced concrete.
4.5.
Microcrete: Fundamentally, hydrated cement paste (HCP) is a nanomaterial (Figure 1). The nano particles size structure of calcium silicate hydrate is much like a clay, with thin layers of solids separated by gel pores filled with interlayer and adsorbed water (Figure 1 ). Microconcrete is a dry ready mix of cementitious based composition formulated for use in repairs of areas where the concrete is damaged and the area is restricted in movement making the placement of conventional concrete difficult. It is supplied as a ready to use dry powder which requires only addition of clean water at site to produce a free flowing non shrink repair micro concrete. This imparts controlled expansion characteristics in the plastic state with reduced water demand.
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Figure 1: Dimensional Range of Solids and Pores in a Hydrated Cement Paste 4.6 Nano-technology and Carbon Nano Tubes (CNT): The term "Nanotechnology" was invented by Taniguchi in 1974, and it was first popularized in the 1980 by scientist and visionary K. Eric Drexler in his book "Engines of Creation." Nanotechnology including Nano ingredients is used for improved mechanical and electrical properties such as higher strength, toughness, flexibility, stability, and conductivity of the material. These are among the most extensively researched Nano-materials today. CNTs are tubular structures of Nano-meter diameter with large aspect ratio. These tubes have attracted much attention in recent years not only for their small dimensions but also for their potential applications in various fields. A single sheet of graphite is called grapheme. A CNT can be produced by curling a graphite sheet. Carbon sheets can also curl in number of ways. CNT can be considered as the most superior carbon fiber ever made. Addition of small amount (1% by wt.) of CNT can drastically improve the mechanical properties consisting of the main Portland cement phase and water. A CNT can be singled or multi walled. CNTs are the strongest and most flexible molecular material with Young’s modulus of over 1 TPa. The approximate diameter is 1 nm with length to micron order. Nanotubes are highly resistant to chemical attack and have a high strength to weight ratio. 4.7 Nano Cement Composites: It consists of Nano size of cement, silica fume, glass particles, aggregates, fibres and admixtures. Grinding of the ingredients is carried out under controlled environment low humidity to avoid agglomeration of particles. Short carbon fibers of size 7 microns, Titanium oxide and Zinc oxide are also added as per the requirement. The product made with NCC is used as an alternate to FRP (Fibre reinforced polymer) repairing cracks etc. 5. Advancements in Concrete Equipment for Construction and Testing The new advancements being carried out by the concrete equipment manufacturing industry are quite significant, keeping the major innovations in view done in the past; and whenever there is a need of higher job volumes, the mobile crushers are being produced. (Figure 2 -4).
Figure 2 Figure 3 Figures 4 Figure 5. Mobile Impact Crusher Mobile Cone Crusher Mobile Jaw Crusher Mobile VSI Crusher Trailer mounted Concrete Pumps and concrete boom placers of 1736 meters have been developed for placing concrete for concrete pavement in hills/remote location (NBMC March 2014). Recently mounted 5
mobile concrete batching plants are being launched driven by a power takeoff from engine; the truck mounted mobile batching plant comes with a capacity of 16 cum/hr. 6. TWO LIFT CONCRETE PAVING There is a potential use of two-lift paving as a sustainable technique for building concrete pavements. Two-lift concrete paving involves the placement of two wet-on-wet layers instead of the homogenous single layer commonly placed in concrete paving. Two-lift paving can provide quality surface characteristics, reduce materials costs, and consume recycled aggregates. (Figure 6) Two-lift concrete pavements have been constructed in the United States for over a century. The first concrete pavement constructed in the United States in 1891 in Bellefontaine, as a two-lift pavement. That pavement is still in service today, as are other two-lift concrete pavements built in the early 1900s.
Figure 6: Two Lift Construction Changes in the availability of aggregates, advances in materials knowledge and construction equipment, and increasing demands for pavement surfaces that meet specific noise less than 100 dB, durability, and safety objectives are prompting the need to reconsider two-lift paving as a construction technique for building concrete pavements. Sustainable solutions are those that balance economic, environmental, and social benefits. The two-lift process has great potential as a sustainable paving solution. It reduces the cost of materials and materials transportation, reduces the environmental impact caused by quarrying and importing aggregates, and increases social benefits by maintaining friction and low noise levels and providing a long-lasting pavement that does not need frequent reconstruction. 7. CONCLUSIONS When compared to conventional concrete pavement, the new types of concrete pavement have better resistance to harsh environment, equal or higher compressive and tensile strengths, higher fire resistance, and rapid curing and strength gain. In addition, the production and life cycle of these new concretes will reduce greenhouse gas emissions by as much as 90%. Researchers in the laboratory using special material (processed sand etc) have achieved “concretes” with compressive strengths in excess of 689 MPa. New equipment is on the rise for getting good concrete product comfortably faster with maximum accuracy. New technology viz two lift paving and similar other techniques reduce consumption of 6
cement, aggregates, steel, and formwork, minimum wastage or pilferage, protection and saving in good agricultural land. Efforts shall be made that the texturing of concrete pavement and its behaviour shall not produce sound between the tyre and finished top surface of concrete road (preferably beyond 70 dB) sound at a height of about 2-3 m. Due to adverse climatic conditions in the border areas, the working season remains very short in the state, resulting in low levels of development. Therefore, it is necessary to bring out urgently or use new materials and techniques to meet special needs of the people of the region for infra-structure development considering prevailing environmental and natural conditions.
REFERENCES i) ii) iii) iv) v) vi) vii)
Taylor, H.F.W., “Cement Chemistry,” 2nd Edition, London, Thomas Telford, 1997 http://www.associationofengineers.com/pdf/51200274e38a44eb7146Latest%20Trends%20in %20Concrete%20Technology.pdf http://www.ecocement21.com/#!home-old/main Advancements in Concrete Equipment, NBMCW March 2012 http: //nanocrete.com/? reqp = Technical Report, Technical Research Institute, Kajima Corporation, Tokyo, Japan http://dx.doi.org/10.1061/(ASCE)0733-9399(1992)118:11(2246) Permalink: http://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9399(1992)118:11(2246) Two-Lift Concrete Paving in Salina/Abiline, Kansas— Interstate 70. December 2009 Gary Fick, Trinity Construction Management, Inc, Federal Highway Administration
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