中文3800字
Preparation of low-cost waterproofing materials
Al—HadidyAI， Ⅳ Yi—qiu，DONG Ze-jiao，WANG Jia—ni
(School of Transportation Science and Engineering,Harbin Institute of Technology,H- arbin 150001,China,E-mail;abd—et76@yahoo.con)
Abstract：To address the need for producing a cheap,single—component,hot-applied compound joint sealant with high quality for sealing joints and cracks in concrete and flexible pavements without using primer for installation,a hot-applied modifled asphalt sealant was produced by blending up about 30％ starch into 20％ citric acid. The starch and the asphalt cement were mixed at a temperature of above 160 ℃.Thus the waterproofing asphalt was manufactured to protect the surface of various shapes and types from water leakage using the citric acid.Results indicate that this sealant complies with the requirements of ASTM D-1191,D-6690-06a and D-71 16-05.The citric acid is a kind of reliable materials for asphalt cement,which can be widely used in paving and waterproofing construction materials,and this offers profound engineering and economic advantages/ Key words：joint sealant；starch；citric acid；waterproofing material；paving asphalt CLC number：U214 Document code：A Article ID：1005-9l13(2008)04-0547-06
1 Background of the Study
The present study relates to waterproofing materials,and in particular to water- proofing asphalt cement and joint sealant.
Joint sealant and waterproofing asphalt is regarded as one of the important primary materials used in the field of civil engineering work.Their selection must always be a matter of compromise between price and performance.For example, Crack treatment,including crack sealing,crack filling,and crack repair,is one of the most common maintenance activities performed on bituminous pavements by local governmental agencies.Crack sealing is the method of placing material in a crack to create a watertight barrier.Transverse and longitudinal crack sealing is performed frequently in order to extend pavement life by preventing or substantially reducing the infiltration of water into the pavement structure.
Sealing cracks in asphalt pavements has long been regarded as an annual preventive maintenance procedure and is expected to have a growth rate of 3％-4％per year.With limited maintenance budgets and increasing labor and material costs,so- me means of reducing the life,cycle cost of crack seals is required.Polymer modified asphalt crack sealer materials,as defined by American Society for Testing and Materials[1,2],have demonstrated the potential to deliver 5 or more years of service life.Because the polymer modifiers that have been employed beneficially as asphalt modifiers are rather expensive，a need exists for alternative,lower-cost modifiers that nonetheless impart improved properties comparable to those achived by using the more expensive polymers.
Highway agencies use different materials and methods to treat cracks in asphah
concrete pavements.Some of these treatments are inherently better than others;howe- ver,the use of starch as a modifier has not been investigated by other researchers in the world.
Substantial quantities of starch are potentially available widely in the world. Starch is a fine white powder mainly composed of two carbohydrate polymers,amy- lose and amylopection.It characterized with low weight is generally much cheaper(0．8$/kg)thanother conventional polymers such as ,styrene-butadiene-styrene,polyethy-
lene,and polypropylene. Starch granule size varies from (1-100)microns in dimeter and shape.On the other hand,beta-hydroxytrisarboxy1ic(citric) acid is a fine white powder with an average partical size of 100 mesh.Citric acid is a very useful and effective preservative,obtained from naturally oecurring organic acids.It consists of 10 ppm heavy meatal,150 ppm sulphate,not more than 0.1 percent sulphate ash,0.2 ppm aluminum,less than 3 ppm ash,and 350 ppm oxalate.These characteristics makes citric acid and starch especially desirable to develop low cost-effective waterproofing materials.
The causes of sealant failure depend on the types of sealant used,installation and service conditions.Sealant as a material can fail due to age and weather exposure．This type of failure is often characterised by discolouration,crazing and stiffening of the sealant surfaces,and is the result of the individual or combined effects of solvent evaporation,ozone attack,migration of plasticisers,ultraviolet radiation,etc.Failure can also occur if there is a large oint movement before the seal is fully cured.In other cases,sealant failures occur because the sealants are required to take cyclic movements beyond their limits.
The various modes of failure experienced with sealants in service are illustrated in Fig.1[3,4].
①Adhesion Failure
This is the most common type of failure due to the loss of bond between the sealant and the substrate(Fig.2)[3,4] . ②Cohesion failure
This is a failure within the sealant material.The effect of movement is likely to make the failure progressive(Fig.3)[3,4] .
③Spalling
This has similar consequences to adhesion failure.It occurs when the cohesive strength of the sealant is greater than that of the surface layers of the material to which it is applied.
④Excessive extrusion
This is ejection from the joint part of which becomes vulnerable to mechanical the sealant,damage impairs the future ability of the sealant remaining joint to perform its function.
⑤Intrusion
This is common in horizontal ioints in traffic areas.It occurs when the sealant surface is penetrated by grit and debris.On subsequent closing，the grit is not ejected,causing abrasion and eventual failure of the sealant and in extreme case impairing the functioning of the joint. ⑥Hardening/weathering/crazing
Hardening of the sealant leads to the formation of cracks crazing.It can be brought about by the loss of solvent or plasticisers and by the action of ultraviolet radiation and ozone. ⑦Softening
Sealant failure caused by softening may be due to improper curing or by thermal/photochemical degradation of the polymer. ⑧Slumping
Sealant flows downwards as a result of gravity.Softened sealants sometimes slump on vertica1 joint.The failure may also result in staining on the facade. ⑨Waisting
A change in sealant shape resulting from viscous flow,which finally leads to thinning of the sealant in a part of the joint.
2 Detailed Description of the Study
The following description is included to demonstrate preferred embodiments of the study.It should be appreciated by those of skill in the art that the method disclosed in the description which follows represent method discovered by the author to function well in the practice of the study,and thus can be considered to constitute preferred mode for its practice.However,those of skill in the art should,in light of the present disclosure,appreciate that one may make many changes in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the scope of the study.
Starch represents an ideal material for inclusion as an asphalt modifier for a number of reasons.First,it exists as microscopic white grains that are insoluble in alcohol,ether,and cold water.Second,it is a highly organized mixture of two carbohydrate polymers,amylose and amylopection .Third,substantial quantities,of starch are potentially available widely in the world at low cost.Finally,unlike many other materials such as used tires.starch comes from its source as a fine,freeflowing powder,which obviates any need for preprocessing the starch before mixing it into the asphalt.On the other hand,citric acid is a potential materials for waterproofing and
being readily available are much cheaper than polymers such as styrene-butidiene-styrene(SBS),etc.
As a result of binder modification with starch and citric acid,the physical and chemical properties of the binder are improved.This improvement takes place because of the change in the chemical properties of the binder.This modification results in higher resistance againstchemicals and fue1.
There is one approach for producing a statch modified asphalt is to blend starch into the asphalt by using hot water (60± l℃ ).Starch granules when heated in water gradually ab sorb water and swell in size,causing the mixture to thicken.With contin- ued heating however,the swollen granule fragments become less thick, and amylose and amylopectin become soluble in the hot mixture.This process of granule swelling and fragmenring is called\gelatinization”.Because of the larger size of the swollen granules compared to the size of amylose and amylopection,the viscosity of the swollen granules mixture is much hi gher than the viscosity of the amylose/amylope- ction mixtures.
In employing this blending method it is extremely important to allow sufficient time to ensure that the starch is uniformly distributed through the asphalt.As a little as 5 minutes or as long as 10 minutes of mixing may be required，depending on the shear rate,which in turn depends 0n the blade configuration of the mixer impeller and the speed of the motor.In addition,it is necessary to continue stirring the blend until it is about to be used.
Citric acid is mixed with asphalt at diferent weight percentages(10％,20％,&30％)for 7 min at temperature of 160 ± 5 ℃ to produce an economically mastic,water proofing and damp proofing asphalt cement.Three modified binders are thus performed from the virgin asphalt.
The Starch jpint sealant samples are prepared in the following procedure;A 20％citric acid modified asphalt that comply with the physical requirements of asphalt mastic(ASTM D-491)is heated to the desired temperature in a three,neck flask provided with stirrer and contact thermometer.The temperature is held constant by an automatic control system while stirring intensively.The starch iS dispersed into the citric acid modified asphalt by using hot water(60±1℃).The resultant asphalt is then combined with filler.The citric acid modified asphalt is treated with different percentages of starch(10,30,and 50 wt％of virgin asphah)and one percentage of calcium carbonate filler (125 wt％of virgin asphalt).The best results are achieved when the blending temperature is maintained above about 160℃ (as shown in Fig.4). 2、1Expermintal
2、1、1Asphalt cement
The test is conducted on asphalt cement according to ASTM[1].The result of these tests are listed in Tab.1.
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