usingadvancesinconcretetec toenhancereadymixsolutions · ready-mixed concrete industry with...

Using Advances in Concrete Tecto Enhance Readymix SolutionsBy Steve Crompton, national technical director, CEMEX UK Materials

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Using Advances in Concrete Technologyto Enhance Readymix Solutions


The last 30 years have seen a dramaticincrease in the availability and use ofsupplementary cementitious materials. Inparticular, the benefits arising from thefollowing materials has led to their usebecoming widespread:

GGrroouunndd ggrraannuullaatteedd bbllaasstt--ffuurrnnaaccee ssllaaggGround granulated blast-furnace slag (ggbs)is a by-product of the production of iron andis formed when molten blast-furnace slag israpidly quenched. The cementitiousproperties of ggbs have long been known(evidence of its first use dates back morethan 80 years) and its use is widespread ina number of countries around the world.It can be interground with cement clinker

to produce a factory-blended cement and thisapproach is common in Europe, although inthe UK ggbs is generally added at theconcrete mixer to produce an equivalentcement combination.Typically, ggbs is used to replace 50% of

the CEM I component of the mix, although inspecialist applications it can be used atreplacement levels of up to 90%.Significant improvements in the resistance

to chloride attack are realized when ggbs isused at replacement levels in excess of40%. Its use also improves the resistance ofconcrete to sulphate attack and this isrecognized in British Standards where theuse of high levels of ggbs replacement isencouraged for the most severe chemical-attack categories.The use of ggbs also reduces the risk of

deleterious alkali-silica reaction (ASR), andagain this is recognized in national guidancedocuments which encourage the use ofggbs where there is potential for ASR.

A further benefit of ggbs is the lower heatof hydration, making its use popular inmass structures to reduce issues associatedwith high temperature development.Not surprisingly, given the potential

benefits of using ggbs, there has been asteady increase in its use in ready-mixedconcrete, although there are implications forthe producer when using the material:• A requirement for additional storagecapacity.

• Additional quality-control requirementsfor the increased range of mixes.

• A small increase in cementitiouscontent where an equivalent 28-daystrength is required.

• Extended setting time, particularly incold weather, can lead to increasedbleeding, although this can be controlledwith the use of admixtures and changesto the mix design.

In general, the use of ggbs presents fewproblems for the ready-mixed concreteproducer and it is the most commonly usedsupplementary cementitious material in theUK.

PPuullvveerriizzeedd ffuueell aasshhPulverized fuel ash (PFA) is a by-product fromthe generation of electricity in coal-firedpower stations, and the pozzolanic reactivityof the material is well documented whenused in conjunction with Portland cements.PFA can be interground with cement

clinker to produce a factory-blended cementor it can be added at the concrete mixer toproduce an equivalent cement combination.Both methods are commonly used in the UK.PFA is generally used at lower

replacement levels than ggbs, typicallyaround 30%, although higher levels are

sometimes used for specific applications.The use of PFA has been shown to improve

the durability of concrete(2) by reducingchloride penetration, improving sulphateresistance and minimizing the risk ofdeleterious ASR. It can also enhance thefresh properties of concrete with reducedwater content leading to less bleeding andimproved flow characteristics.The use of PFA has continued to increase

although the cyclical availability of thematerial has restricted its growth comparedwith ggbs.From a ready-mixed concrete perspective,

there are some implications when using PFA:• A requirement for additional storagecapacity and a need for enhancedaeration on silos to handle the finernature of PFA when compared withcement or ggbs.

• Additional quality-control requirementsfor the increased range of mixes.

• An increase in cementitious contentwhere an equivalent 28-day strength isrequired. These incremental increasesare somewhat larger than those seenwith ggbs and can be up to 40kg/m3.

MMiiccrroossiilliiccaaMicrosilica is a by-product from theproduction of silicon and ferrosilicon. It is avery fine, highly reactive, high-SiO2 pozzolanwhich significantly reduces the porosity of theconcrete.Microsilica is typically used as an addition

to enhance the properties of high-performance concretes and is used ataddition rates of between 5 and 20% byweight of cement.Microsilica has been shown to improve

durability, abrasion resistance and thestrength performance of concrete, but thematerial is significantly more expensivethan cement and its use is largely restrictedto specialist applications or high-strengthconcretes (typically >80N/mm2).

MMeettaakkaaoolliinnMetakaolin is manufactured from calciningkaolin at temperatures between 700–900°Cto produce a highly reactive pozzolan whenmixed with CEM I. It is typically used in asimilar way to microsilica, ie as an addition(5–15% by weight of cement) to produce high-performance concrete.Limited availability and field experience

with metakaolin has led to a lower rate ofusage than other mineral additions, such asggbs, PFA and microsilica. However, researchdata indicates performance levels similar tothose seen with microsilica.

SSuummmmaarryyConsiderable research and field experiencehas demonstrated that the use of mineraladditions enhances the performance ofconcrete by improving a number of keyproperties. This has been recognized inBritish and European Standards, withdesigners increasingly specifying the use of

An estimated 75% of all ready-mixed concretes now contain a mineral addition

Concrete Technology


such materials. The ready-mixed concreteindustry has responded by making suchmaterials widely available and an estimated75% of all ready-mixed concretes nowcontain a mineral addition.

AADDMMIIXXTTUURREE TTEECCHHNNOOLLOOGGYYPerhaps the most significant advances inconcrete technology have been in the field ofadmixtures, which has permitted thedevelopment of a range of high-performanceconcretes that has allowed designers tofully exploit the benefits of the material. Themajor admixture companies invest heavily inresearch and development, and during thelast 30 years there has been significantincrease in the range of admixtures availableto both the cement manufacturer and theready-mixed concrete producer:

WWaatteerr--rreedduucciinngg aaddmmiixxttuurreessThese are the most commonly usedadmixtures, typically added to reduce watercontent while maintaining workability andthereby reducing the cement content for agiven strength.

HHiigghh--rraannggee wwaatteerr rreedduucceerrssIncreasingly used to increase the consistenceof concrete while maintaining strength.Arguably, the most significant advanceshave occurred in this area of admixturetechnology with the development ofpolycarboxylate ether (PCE)-based products.These have led to the development of self-compacting concrete and have been criticalin the achievement of ever greater concretestrengths. PCE admixtures can bemanipulated to modify their impact onimportant properties of concrete, such ascohesion, rate of strength gain, consistencyand slump retention.

VViissccoossiittyy--mmooddiiffyyiinngg aaggeennttssViscosity-modifying agents have beendeveloped to maintain cohesion at very highconsistency values and are routinely used in

the manufacture of self-compactingconcrete.

GGrriinnddiinngg aaiiddssGrinding aids that optimize the cementmanufacturing process and reduce energyconsumption are now commonplacealongside chemicals that enhance thestrength performance of cement.

SShhrriinnkkaaggee--ccoommppeennssaattiinnggaaddmmiixxttuurreessThis range of admixtures reduces theinherent shrinkage of concrete, which is aninevitable result of the hydration process. Useof these admixtures is particularly beneficialin the construction of concrete floors, wherethey permits much wider joint spacing. Inconjunction with other technologicaldevelopments, such as steel fibre, they caneven be used to produce ‘jointless’ floors.

CCoorrrroossiioonn iinnhhiibbiittoorrssAdditional resistance to the corrosion ofreinforcement can be obtained by the

incorporation of corrosion inhibitors in theconcrete, and such admixtures are often usedin critical projects.

PPiiggmmeennttssPigments come in a wide range of coloursand give artistic licence to designers,allowing them to use concrete in manydifferent ways.

WWaatteerr--pprrooooffiinngg aaddmmiixxttuurreessPore blockers are increasingly being used inthe design and construction of waterproofstructures and there is continualdevelopment in this area to improve theperformance of such admixtures, particularlywhere concrete is subjected to externallyapplied water pressure.The above list is by no means exhaustive

and other admixtures, such as retarders andair-entrainers, are routinely used to modifythe fresh and hardened properties ofconcrete.The benefits of admixtures in increasing

durability, improving placing times, reducingcosts and improving the sustainabilitycredentials of concrete are widelyacknowledged, and the growth in the use ofadmixtures reflects this with the volume ofsales in the UK trebling over the last 15 years,as shown in figure 1.In the ready-mixed concrete industry, it is

now the exception rather than the rule forconcrete to be produced without anadmixture, and an increasing proportionincorporates high-range water reducingadmixtures (HRWRA), which is also reflectedin figure 1.

FFIIBBRREE TTEECCHHNNOOLLOOGGYYThe use of fibres in concrete and mortar isnot new, as evidenced by the use of animalfibres in some of the earliest recordedconcretes. As with admixtures, there havebeen significant developments in the type,availability and performance of fibres, andthere are three generic types of fibreavailable in the market: �

Fig. 1. Growth of admixture sales in the UK

Fibres are widely used in ready-mixed concrete for tunnelling applications


SStteeeell ffiibbrreessSteel fibres are produced in a range ofshapes and sizes, and although generallymanufactured from mild steel they areavailable in stainless steel and in galvanizedform. They are typically added at dosagerates of between 15–50kg/m3 depending onthe type of fibre and desired properties of theconcrete.Steel fibres can increase the toughness

and ductility of concrete and are widelyused in industrial flooring applicationsthroughout the world. More recently,composite construction techniques havebeen developed which allow steel fibre toreplace traditional structural reinforcementin some applications.Steel fibre concrete is available from

most ready-mixed plants across the UK,although a few days’ notice may be requiredto ensure that the specified fibre is in stockat the plant. It is essential to ensure that thefibres are fully dispersed in the concrete andit is common for steel-fibre concrete toalso include a high-range water-reducingadmixture to enhance the consistency of theconcrete and facilitate thorough mixing.

PPoollyypprrooppyylleennee ffiibbrreessPolypropylene fibres are generallyincorporated at much lower dosage ratesthan steel fibres, typically less than 1kg/m3,

and are essentially used to modify the plasticproperties of concrete to minimize plasticcracking problems. They also contribute toimproved abrasion resistance, enhancedimpact resistance and increased spallingresistance in fires.The use of polypropylene fibres has grown

steadily since the 1980s and estimatessuggest that over 5% of all ready-mixedconcrete in the UK now incorporates suchfibres. From a producer’s perspective, thefibres are easy to handle and easy to add tothe concrete, although care is required toensure that the effects on consistencystrength are accounted for.

SSyynntthheettiicc mmaaccrroo ffiibbrreessSynthetic macro fibres are a more recentdevelopment and are generally manufacturedfrom blends of various organic polymers,including polyethylene and polyolefins(3).Recent developments have allowed themanufacture of higher-modulus materialswith a variety of anchorage mechanisms thatenhance bonding and lead to improvedperformance of this type of fibre.Although relatively new to the UK, their

reduced dosage rates (typically 2–7kg/m3)make them popular with ready-mixedconcrete producers as they can be easier tohandle than steel fibres. Their use inapplications such as industrial flooring andcomposite steel decking continues toincrease.Combinations of fibre types can also be

used to realize the plastic-state benefitsprovided by polypropylene fibres coupled withthe hardened-state benefits that areassociated with the use of steel or syntheticmacro fibres.

SSUUSSTTAAIINNAABBIILLIITTYYThe concept of sustainability has become animportant topic in all areas of constructionand the production of ready-mixed concreteis no exception(4). Sustainability will becomea major driver for the future development ofcementitious materials and increasinglycompanies will be looking to reduce theenvironmental impact of their products.Sustainability can be considered to be the

combination of social, economic andenvironmental impacts, and together theseinfluence how a product is viewed. Asustainable material needs to demonstrate: • Minimal damage to the environment (renewable, non-toxic,recyclable, biodegradable etc).

• Minimal waste associated with its use(waste in manufacture; over-ordering;off-site pre-assembly etc).

• Local supply (if found locally, travel keptto a minimum, reducing harmful fuelemissions).

• Low embodied CO2 emissions (accountfor all emissions during sourcing,manufacturing and life cycle of amaterial/product).

In addition, a sustainable material mustalso be durable, robust, resistant to fire and

Advanced polymer fibres

Sustainability will be a major driver for the future development of cementitious materials


provide adequate security.The ready-mixed concrete industry has

responded to these challenges by:

Reducing pollution andemissions—dust emissions cut by 90% over the last 20 years

—18% reduction in carbon dioxide to air—46% reduction in sulphur dioxide—17% reduction in oxides of nitrogen—60% saving in particulate matter.

Increased use of recycled rawmaterials—The UK cement and concrete industry iscontinuing to contribute to the UK WasteStrategy by consuming waste produced byother industries and recycling its ownwaste

—The cement industry is playing animportant role in minimizing some of thecountry’s waste-disposal problems byprocessing selected wastes into alternativekiln fuels

—The use of ggbs and fly ash in concrete andcement is increasing, allowing a reductionin CO2 emissions of up to 45%.

Reduced waste and increasedefficiency—compliance with strict environmentallegislation

—ISO 14001 accreditation becoming thenorm

—concrete plants now recycle water (up to65% is achievable)

—across the EU, specific energy consumptionin the production of cement clinker hasreduced by 30% since the 1970s.

Less reliance on primaryminerals—1.5 million tonnes of ggbs and fly ash usedin UK each year as cementitiousreplacement

—reduction in CO2 emissions by 1.5 milliontonnes

—reduction in primary energy usage by2,000 million kilowatts per hour

—saving 1.5 million tonnes of quarrying—saving 1.5 million tonnes of landfill.

Reduced use of primaryaggregates—45% decrease in the production of primaryaggregates from 1989–2011

—94% increase in use of recycled andsecondary aggregates

—By 2011, 30% of aggregates (70 milliontonnes) will come from non-primarysources.The industry is aware of its responsibilities

in relation to sustainability issues andcontinues to invest time, money andresources to further improve its performancein this important area. Although concrete isa small net contributor to global warming,

responsible for only 2.6% of UK CO2

emissions in 2006, it continues to promotethe use of materials and technologies thatwill further reduce its impact on society(5).

MMIIXX DDEESSIIGGNNTo make the most of the developmentshighlighted above requires the concretetechnologist to tailor mix designs to meet therequirements of the specifier, and this ishighlighted here by considering threeapplications that have developed as a resultof advances in concrete technology:

HHiigghh--ssttrreennggtthh ccoonnccrreetteeThe specified strength of concrete hassteadily increased over the last 30 years.During this period average strengths haverisen by around 10N/mm2 and an increasingamount of all concrete is specified bystrength characteristics.A more dramatic increase has been seen

in the development of high-strengthconcretes. Whereas C50 was once consideredto be high strength, it is now commonplaceto see C80 concretes routinely produced andstrengths up to C130 have been produced bysome ready-mixed concrete plants.These strengths are only possible by the

careful selection and combination of rawmaterials and the utilization of high-rangewater-reducing admixtures in combinationwith selected cementitious components,such as PFA and microsilica. Particle packingtheory and the rheological behaviour of theconcrete become important parts of themix-design process in these applications.The boundaries of high-strength concrete

have been pushed further with thedevelopment and production of ultra-high-strength concretes, where strengths canexceed 200N/mm2, although to date there is

limited application and production of suchmaterials.

SSeellff--ccoommppaaccttiinngg ccoonnccrreetteeSelf-compacting concrete (SCC) hasdeveloped rapidly since it was firstdemonstrated in Japan in the late 1980s.Developments in admixture technology anda better understanding of the rheologicalcharacteristics of SCC have allowedproducers to reliably produce materialswhich can be placed without vibration,leading to benefits from increasedefficiencies on site, reduced environmentalimpact and improved surface finish.However, the design of SCC is complex,

often including multiple powder andadmixture combinations to ensure that thedesired properties are achieved, and furtherresearch and development is required toensure greater robustness of the mixdesigns.

DDeessiiggnniinngg ffoorr ssuussttaaiinnaabbiilliittyyThe use of secondary cementitiouscomponents is commonplace in the industryand the use of such materials can reduce theCO2 footprint of concrete by up to 40%.Water-reducing admixtures are routinely

used to reduce water contents and therebypresent opportunities to meet specifiedstrength requirements with lower cementcontents.The use of recycled water and the

elimination of wash-out waste is now thebenchmark in the industry, and largerproduction units will have reclaimer facilitiesto recover materials from any returnedconcrete.The use of recycled aggregates is often

seen as a logical way of reducing theenvironmental impact of concrete. �

Concrete Technology

Self-compacting concrete has developed rapidly since it was first demonstrated in Japan in the late 1980s


However, the use of recycled aggregate(RA) or recycled concrete aggregate (RCA)needs careful consideration, as their use cansignificantly increase the cement content.Detailed consideration of the overall

sustainability benefits of using RA or RCA isrequired to ensure that the full impact onsustainability is understood, as it is often thecase that locally sourced natural aggregateis a more sustainable solution than theimportation of recycled materials.

PPRROODDUUCCTTIIOONNTTEECCHHNNOOLLOOGGYYThe basic requirements for producingconcrete are little different today than whenthe industry was born almost 80 years ago– the homogeneous mixing of cement,aggregates and water to produce a materialthat can be transported for up to 2h and stillbe usable at the construction site.However, the world has changed and

developments in cement and concretetechnology have led to increasingly complexmixtures requiring ever more sophisticatedmixing and control techniques to meet thedemands of modern-day constructionmethods.Computerization, advances in material

measurement and the availability ofadvanced admixtures allow the ready-mixedconcrete producer to design and produce ahuge array of complex, technicallydemanding concretes that were simply

unachievable even 10 years ago.Increasing environmental awareness has

driven significant changes to the design ofmodern concrete production units, with newplants being totally enclosed and no wasteever leaving site as concrete and waterrecycling units become the norm.From the outside, a modern concrete

production plant may not look very differentto those built 60 years ago, but the technologyand sophistication of the modern plant andthe materials it produces are light years fromthe first plant built in the UK in 1930.

CCOONNCCLLUUSSIIOONNSSThe last 30 years have seen many innovationsin the field of concrete technology,particularly relating to the development ofalternative cementitious components andever more powerful and flexible admixturesystems capable of modifying the fresh andhardened properties of concrete.More recently, the focus on environmental

issues and the concept of sustainabilityhave led to changes in the way that rawmaterials for concrete production aremanufactured and used. There has been anincrease in the use of recycled and alternativematerials which, together, can reduce theenvironmental impact of concrete, andfurther developments in this area areexpected.These developments have been adopted by

the ready-mixed concrete industry and the

nature of the products produced by theindustry has changed significantly.Production units are now more sophisticated,stocking a broader range of cements,admixtures and aggregates that allow theproduction of a wide range of high-specification concretes engineered to meetthe most demanding applications.

RREEFFEERREENNCCEESS1. SCRIVENER, K.L., and R.J. KIRKPATRICK:‘Innovation in use and research oncementitious material’, Cement and Concrete Research 38 (2008), pp128-136.

2. BAMFORTH, P.B.: ‘Enhancing ReinforcedConcrete Durability’, Concrete SocietyTechnical Report No. 61, 2004.

3. Guidance on the use of macro synthetic-fibre-reinforced concrete, Technical ReportNo.65, 2007.

4. Guidance Document on ‘SustainableConcrete Design and rating Systems’, British Ready-Mixed Concrete Association,2008.

5. MEYER, C.: ‘The greening of the concreteindustry’, Cement and ConcreteComposites, 2009.This paper was presented at the 37th

Annual Technical Symposium of the Instituteof Concrete Technology (ICT) in April 2009and subsequently published in the 2009/10edition of the ICT Yearbook. It is reproducedhere by kind permission of the ICT.

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Today a wide range of high-specification concretes meet the most demanding construction applications

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