文稿教程講稿pad longv1

1、Subgrade Stabilisation using Chemical AgentsIntroductionThe subgrade of a pavement experiences low forces as they are distributed over a larger area when they reach it.If it is weak it can deform and damage the entire pavement.The subgrade is also the initial work platform on which the rest of the p

2、avement is constructed.Weak soils such as fine grained sand and clay are very common.When weak soils are encountered they must either be replaced or remediated before construction can begin.IntroductionCommon ways to improve subgrade include borrowing stronger material from elsewhere on site, import

3、ing stronger material from outside sources, granular stabilisation, and chemical stabilisation.Replacing the material and granular stabilisation involve removal and disposal of the unwanted material, so take up a lot of space, time and money.Chemical stabilisation uses the in-situ material, strength

4、ens it, and reduces its reactivity to the environment, such as shrink swell with water content.The effects of the chemicals are quick so the rest of the work can begin rapidly.Commonly used chemical agents are lime, cement, fly ash, ground granulated blast furnace slag, dry powdered polymers, and ki

5、ln dusts.LimeLime has been used as a stabilising agent for weak cohesive soils since the 1930s.Hydration reactions use up water, dry out the soil, create heat, and flocculate the particles together.The dryer material with a larger grain size produces an easily compactible material with a higher bear

6、ing capacity.It is used in 2 main forms quicklime which is calcium oxide (CaO) and hydrated lime which is calcium hydroxide (CaOH2).LimeQuicklime is formed by the chemical breakdown of limestone under high temperatures in a kiln.Hydrated lime forms when quicklime is mixed with water, then dried out.

7、Lime may also come as agricultural lime, a finely ground limestone with low reactivity or lime kiln dust.Lime kiln dust, similar to cement kiln dust which will be discussed later is a pozzolanic material extracted from the exhaust gases from the kiln during quicklime production.LimeLime can be used

8、to either dry and modify the soil or fully stabilise it.Modifying and drying involves adding 1% to 4% of the dry weight of soil as lime, it is often used around construction sites when problematic soils makes it difficult for plant to get around.When added as quicklime the hydration reaction uses up

9、 water and causes heat which further dries the soil, the hydrated lime then reacts with the dry clay particles and flocculates them.When added as hydrated lime, it reacts with the clay to flocculate the particles, removing water from the clay matrix and creating larger particles.The dry large partic

10、les are easy to compact and less reactive to water.LimeFull stabilisation occurs at amounts over 5% of the dry weight, at an amount sufficient to raise the pH to 12.4.The higher pH breaks down the clay, allowing more clay to participate in reactions and form a strong cementitious matrix when allowed

11、 to cure.LimeIt can be introduced to the soil as a powder or slurry.When added as a powder water is added and it is mixed thoroughly and compacted in multiple stages and then allowed to cure.When added as a slurry there is no need to add water, multiple applications may be necessary due to the low l

12、ime content in the slurry, typically 42% solids.Full stabilisation usually involves more thorough mixing and testing than simple drying and modification.LimeWhen in powder form it can be spread evenly by self unloading trucks.Quicklime is granular, and hydrated lime is a fine powder.The fine powder

13、is easily removed by wind, and so needs to be quickly saturated and mixed, especially in urban areas or next to an active road.Slurries can be applied by tankers, with internal augers to keep the solids suspended.Water is applied to the powders directly before mixing to prevent run off.Initial mixin

14、g can be plished by a rotary mixer or a grader with a scarifier attachment.LimeThe soil can be ripped or scarified before lime application to provide a larger surface area for initial contact, and to help with runoff.Modern mixing equipment and processes often make this unnecessary.After mixing the

15、soil should be lightly compacted to preserve moisture and left alone for a 1 to 2 days.This is called the mellowing stage, when some curing can take place give the fine particle time to flocculate.LimeA visual and physical inspection is required to determine if any water should be added before final

16、 mixing.Final mixing should occur with a rotary mixer until it appears mostly granular and no pockets of lime or clay remain.Final compaction should be done with heavy rollers to the desired density and surface profile.Up to a week of curing should be provided where the surface is kept moist by eith

17、er regular watering or with a thin bituminous coating.LimeLime stabilisation is ideal for cohesive soils that have a plasticity index greater than 10 and greater than 25% of material passign through the 0.074 mm sieve.It is unsuitable for soils that have greater than 1% organic matter and greater th

18、an 0.3% sulphates.Clay soils are often found in coastal areas and low lying regions globally.Clay is a very fine grained material, and very reactive to water with a high shrink and swell capacity as the moisture content varies.When wet it is highly plastic and difficult to work with and has a low be

19、aring capacity.It is therefore unsuitable to construct pavement on and should be improved or replaced.Case Study: I-20 Reconstruction GeorgiaIn 2007, the Georgia Department of Transportation in the USA began to investigate the reconstruction and widening of a significant length of the Interstate 20

20、(I-20).Geotechnical investigations were performed and concluded that the in-situ subgrade material was a deep layer of wet highly plastic clay.Case Study: I-20 Reconstruction GeorgiaThree options were considered and a cost analysis was conducted to decide on the action to take.First removal of 600mm

21、 of material and replacing it with more suitable material, unsuitable because of the work involved and possible damage to adjoining roads.Second a 150mm thick graded aggregate base.Last lime stabilising a 230mm thick top layer.Case Study: I-20 Reconstruction GeorgiaThe cost analysis showed that lime

22、 was the cheapest option.The job was tendered and completed.The physical properties after stabilisation can be seen in the figure to the right.Lime was obviously the most suitable option because of the clay.The results show the benefits.Cement stabiliserwhat is it?In general is referred to the organ

23、ic and inorganic binders, which the hydraulic cements are the most widely knownHydraulic cement act as a binder by reacting with the water and during the hardening process, it provides bonding within the inorganic materials thus to form a stable and durable product.The most common types of cement in

24、cludes type GP-general purpose portland cement and type GB- general purpose blended cement.General purpose cements are produced from a mixture of calcium carbonate, aluminia, silica and iron oxide which, when calcined and sintered at high temperatures gives a new group of chemical compounds capable

25、of reacting with water. Cement stabiliser General purpose portland cementHomogeneous product while portland cement clinker and calcium sulphate mixed together.Hydrated silicates and calcium hydroxide are formed while water is hydrated by the cement.General purpose blended cementGeneral purpose portl

26、and cement is either containing:more than five percent of fly ash or ground granulated iron blast furnace slagless than ten percent silica fumeCement stabiliserThe theory behind cement stabilisation is to mix cement and water with pavement aggregate to increase the pavements load bearing capacity an

27、d stiffnessCement stabiliser has been applied for the pavement subgrade construction since 1935.Have been used to improve the strength of the pavement and repair road failures in the existing pavements For the new pavements, cement stabiliser is applied to reduce the sensitivity to moisture. Cement

28、stabiliserHow is it used? Portland cementcan be used to stabilise large range of soils, from granular soils to low plasticity clays. Highly plastic clays are most effectively stabilized with lime.The guideline of application of portland cement stabiliser is published by the Portland Cement Associati

29、on (PCA).Portland cement stabiliser is not applicable:the gravel soils exceed 45 percent of soils aggregates larger than 4 sievesoil Plasticity Index higher than 20 Portland cement would be suitable for heavier clays if the clay is treated with lime or fly ashCement stabiliserHow is it used?Soils st

30、rength, plasticity index and swell characteristic would be modified by using small amount of portland cement.strength of various soils stabilised with general purpose cement ( Metcalf, 1977)How is it used? (Portland cement) CONBy properly mixing the soil which plasticity index higher than 20 with ce

31、rtain extent of cement will produce a uniform, continuous and stable matrix coalescence.Mixing time for the cement before compaction of the pavement subgrade should not exceed two hours.For the plasticity index of less than 30 clay soil, cement does not necessarily cover all particle to successfully

32、 stabilise due to the formation of stable clay particle surrounding matrix by the cement. The durability of matrix will begin to reduce if the amount of aggregate around portland cement is violated.How is it used? (Portland cement) CONThe sulfate content and organic matter content are the two elemen

33、ts of determining whether portland cement is a suitable stabiliser or not. Higher cement content may be needed for the high organic matter content soil to prevent normal quenching process (Little D, 2009). Its important to consider applying the amount of cement before stabilise the pavement subgrade

34、 by portland cement.Moisture density relationship of the soil and soil type are two main factor to determine the amount of cement.Cement stabiliser: Method of applicationThe aggregate can be classified as unbound, modified and bound based on the amount of cement stabiliser added.classification of st

35、abilisation types. ( Cement & Concrete Association of New Zealand )Cement stabiliser: Method of applicationThe tensile strength is introduced to distinguish the different types material after ater stabilisation. There is no cement or other binder exist in the unbound material thus they have no tensi

36、le strength. The modified material is usually containing less than 2% of cement, while bound material is typically containing more than 3% of cement. Modified materials has high shear strength but their tensile strength is also able to prevent fatigue cracking.Shrinkage cracking may occur during cur

37、ing for the bound material. The unconfined compressive strength for modified material is between 0.7MPa to 1.5MPa while for bound material is greater than 3MPa. Cement stabiliser: Method of applicationMaterials for modified can either be quarried granular material or recycled in-situ pavement but fo

38、r bound material only quarried granular material can be used. In construction, Cement and water are plant mixed with quarried granular materials. The mixed modified material is stockpiled for 7 days then turned and moved to a second stockpile, where it can be stored for a further 90 days. For the bo

39、und material, Cement and water are plant mixed with quarried granular materials and used in the pavement within 2 hours of manufacture.Cement stabiliser: Method of application Spreading Cement over Subgrade Mixing, and compaction process of PC-stabilized subgradeCement stabiliser: Method of applicat

40、ionModified materials are commonly used in high traffic volume road such as state highways as it can be used to improve resistance to deformation and rutting.Low quality aggregates can be used to be modified materials.Bound materials are ideal for the heavily loaded roads.Its commonly used under rig

41、id concrete pavements as it provide high strength to support the thick overlying chip seal surfacing layers.Cement stabiliser:Why it is used?Cement stabilisation is widely used to improve pavement performance as it not only provide advantage at the economical aspect, but also its considered to be en

42、vironmental friendly. Stabilised subgrade is able to be trafficked during construction if needed. So the costs for the unforeseen disruption to traffic could be minimised if construction program is delayed.cement stabiliser can be applied to reduce the sensitivity to moisture, it will reduce risks o

43、f loss bearing capacity in wet conditions. Therefore the ability of resisting rutting and other types of deformation is improved.Cement stabiliser:Why it is used?Ability of moisture resistance will also benefit in reduce the risk of water penetration to cause soften of pavement. As a result, the dur

44、ability of road surface is increased and decrease the need of maintenance.By applying cement stabiliser efficiently can reduce the overall pavement thickness. From the environmental aspect, cement stabilisation require low quality aggregates, therefore premium quality aggregates can be conserved and

45、 the existing pavement material can be recycled.It reduces the transportation of aggregates to site if the region is lack of quality aggregate source, thus the fuel consumption , traffic congestion and pavement wear will be minimised. Fly AshWhat is it？How it is used？AdvantagesFly AshFly ash, also k

46、nown as flue-ash, is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gasesFly AshFly ash is a heterogeneous material. SiO2, Al2O3, Fe2O3 and occasionally CaO are the main chemical components present in fly ashes.Fly AshClass F fly ash, which is m

47、ostly used as one of the paving material, produced by burning of harder, older anthracite and bituminous coal. Fly AshHow it is used？Portland cementEmbankmentSoil stabilizationFlowable fillAsphalt concreteGeopolymersRoller compacted concreteBricksMatal matrix compositesWaste treatment and stabilizat

48、ionFly AshAdvantagesGreater strengthDecreased permeabilityIncreased durabilityReduced alkali silica reactivityReduced heat of hydrationReduced efflorescenceGGBFSGround Granulated Blast Furnace SlagIntroductionApplicationBenefitsGGBFSGGBFS, which is short for Ground Granulated Blast Furnace Slag, mai

49、nly contain CaO (30-50%), SiO2 (28-38%), Al2O3 (8-24%), and MgO (1-18%).GGBFSGGBFS is used to make durable concrete structures in combination with ordinary portland cement or other pozzolanic materials. GGBFS has been widely used in Europe, and increasingly in the United States and in Asia (particul

50、arly in Japan and Singapore) for its superiority in concrete durability, extending the lifespan of buildings from fifty years to a hundred years. GGBFSPortland blast-furnace cement (PBFC) High-slag blast-furnace cement (HSBFC)GGBFSAdvantagesEnvironmentalReduced risk of crackingIncreased long term st

51、rengthImproved durabilityDDPA dry powdered road stabilising binder consisting of an insoluble polymer thermally bound to a very fine carrier such as fly ash. The Australian Stabilising Industry Association (AustStab) (1998) This comprehensive definition avoids confusion with water-soluble stabiliser

52、s that are sometimes referred to as polymers.The DPP consists of an insoluble polymer thermally bound to an inert fine carrier, which is then added to small percentages of hydrated lime. The lime is not coated with polymer. DPPHow it is usedBecause DPP stabilisation does not involve a cementitious c

53、hemical reaction, the incorporation of DPP is not associated with a time constraint during mixing and achieving compaction as occurs with other binders.Most road gravels have sufficient strength to resist typical traffic stresses when dry however, they dramatically lose strength when wetted up. When

54、 wet clay and silt fines within gravels e greasy they lubricate the larger aggregates resulting in permanent plastic deformation.DPPs act to preserve the adequate dry strength of water-susceptible gravels by a process of internal waterproofing. This involves creating a hydrophobic soil matrix betwee

55、n the aggregates, which reduces permeability, and limits water ingress. The typical softening and lubricating effect of any moisture that enters a granular pavement is also significantly reduced (internal waterproofing).DPPHow it is iusedA view of a pavement material sample unstabilised (left) and s

56、tabilised with DPP (right) subject to soaking in water for 24 hours. DPPWhy it is usedDPP stabilisation is especially suited for treating moderate to poor quality gravels that lose considerable strength when wetted up. They also have particular application to regions of high water tables, periodic f

57、looding of pavements and even during prolonged drought periods.The field performance of DPP stabilised pavements has shown to increase pavement rut resistance (less moisture sensitive) for granular materials that historically were highly sensitive to moisture. The subgrade is also further protected

58、because there is minimal to no deformation of the stabilised pavement itself. It is important for a stabilised pavement to function as an impermeable protection of the subgrade to improve its volume stability.DPP stabilised pavements have reduced deformability and functions as a low permeability pro

59、tective barrier to the subgrade.CKDCement kiln dust is created in the kiln during the production of cement clinker. CKDRecently, has been a trend of utilizing CKD in soil stabilization, sewage treatment, etc. In this study attempts are made at utilizing it as partial replacement of Portland cement i

60、n mortar and concrete production.The CKD and Portland cement are characterized from a chemical, mineralogical and physical point of view. Several blends of binding materials are prepared using 0-45% CKD as partial replacement of Portland cement. In addition to CKD, in some other blends, fly ash and