influence of hardened cement paste content on the water absorption
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Influence of hardened cement pastecontent on the water absorption of finerecycled concrete aggregatesZengfeng Zhao a b , Sébastien Remond a b , Denis Damidot a b &Weiya Xu ca Université Lille Nord de France , Lille , Franceb Civil and Environmental Engineering Department , Mines Douai,LGCgE GCE , Douai , Francec Geotechnical Research Institute , Hohai University , Nanjing ,ChinaPublished online: 01 Jul 2013.
To cite this article: Journal of Sustainable Cement-Based Materials (2013): Influence of hardenedcement paste content on the water absorption of fine recycled concrete aggregates, Journal ofSustainable Cement-Based Materials, DOI: 10.1080/21650373.2013.812942
To link to this article: http://dx.doi.org/10.1080/21650373.2013.812942
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Influence of hardened cement paste content on the water absorptionof fine recycled concrete aggregates
Zengfeng Zhaoa,b, Sébastien Remonda,b, Denis Damidota,b* and Weiya Xuc
aUniversité Lille Nord de France, Lille, France; bCivil and Environmental EngineeringDepartment, Mines Douai, LGCgE GCE, Douai, France; cGeotechnical Research Institute, Hohai
University, Nanjing, China
(Received 31 March 2013; final version received 5 June 2013)
A linear relationship was found between the mean size of four granular classes(0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5mm) of different laboratory-made fine recycledconcrete aggregates (FRCA) and their hardened cement paste content (CPC).A method based on salicylic acid dissolution was specifically developed for themeasurement of CPC. Results showed that bound water and density of FRCA werestrongly correlated with their CPC. Identically, the water absorption coefficient alsofollowed a linear trend as a function of the CPC but only for the three coarsergranular classes. Indeed, the water absorption coefficient of the finer fraction ofFRCA (0/0.63mm) cannot be correctly measured using European standard methodEN 1097-6 or method no. 78 of IFSTTAR; but it can be obtained by extrapolationfrom the previous linear trend. As a consequence, the accurate total water absorptionof FRCA (fraction 0/5mm) can be estimated.
Keywords: cement paste; recycled concrete aggregates; water absorption; salicylicacid; granular class; porosity
1. Introduction
With the rapid development of construc-tion industry, lots of construction anddemolition wastes (C&DW) are generatedyearly in the world.[1–4] Meanwhile, goodquality natural aggregates (NA) are inshortage. Up to now, only a small propor-tion of C&DW is reused. Components ofC&DW typically include concrete, wood,metals, gypsum, asphalt, bricks, and othermaterials.[5–7] Old concrete is the mostabundant material among various types ofC&DW. The use of recycled concreteaggregates (RCA) crushed from oldconcrete to replace or partially replace theNA has become more common.
RCA are mainly composed of anintimate mix between NA and cement
paste and the complete separationbetween these two phases seems to be adifficult task. Cement paste generally pre-sents a much larger porosity than NA; thecontent and the physicochemical proper-ties of cement paste, therefore, have alarge influence on the properties of RCA.The coarse fraction of RCA (CRCA),essentially composed of natural gravel,generally possesses satisfying propertiesfor the reuse as concrete aggregates. Lotsof studies [8–11] have been dedicated totheir characterization and to the study ofproperties of concretes containing CRCA.However, the fine fraction of RCA(FRCA), containing a larger content ofmortar and cement paste, possesses alarge water demand which makes it harder
*Corresponding author. Email: [email protected]
Journal of Sustainable Cement-Based Materials, 2013http://dx.doi.org/10.1080/21650373.2013.812942
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to recycle into concrete. Concrete manu-factured with FRCA generally presents alower workability, a lower strength, and alesser durability than similar concretecomposed of NA.[12–15] However, muchless studies have been dedicated toFRCA, and there is in particular no gen-eral study on the quantitative influence ofcement paste content (CPC) on the otherproperties of FRCA.[16]
Up to now, there is no standard testto measure CPC in RCA; however,different methods have been found in theliterature:
• Thermal treatment [17]: this methodis based on several cycles of soak-ing in water and heating of theaggregates, which allows detachingprogressively adherent mortar fromcoarse aggregates surface becauseof micro-cracks occurring at theinterface between aggregates andmortar. This method is only suit-able for CRCA because theremoval of mortar necessitates“brushing” the RCA, which is diffi-cult with small particles.
• Treatment with a solution of hydro-chloric acid [18]: this method isbased on the dissolution of cementpaste in a solution of hydrochloricacid. Unfortunately, it cannot beused with limestone aggregates andfiller, which is also dissolved byhydrochloric acid.
• Image analysis [19]: image analysisis used to quantify the amount ofresidual mortar on flat polished sec-tion. This method is suitable forquantification of residual mortar inCRCA, but the distinction betweenfine aggregates and cement paste ismore difficult to carry out. More-over, this method is long to performas a statistical approach is needed.
None of the above-mentionedmethods seems to be adapted to the
characterization of CPC in FRCA, espe-cially for RCA containing calcareousaggregates. However, CPC in FRCA isclosely related to the water absorption ofFRCA that plays an important role in themanufacture of concrete. Indeed, it has tobe measured precisely in order to deter-mine the efficient water content in con-crete. However, the methods used tomeasure the water absorption coefficientof fine aggregates are generally not accu-rate for materials containing large frac-tions of fine particles.[20–21]
The objectives of this paper are thefollowing:
(1) develop a simple method forthe measurement of CPC ofFRCA;
(2) relate the CPC to different physi-cal properties such as the waterabsorption coefficient as a func-tion of four different granular clas-ses (0/0.63, 0.63/1.25, 1.25/2.5,2.5/5mm; here, for example, 0.63/1.25mm stands for the minimumand maximum particle sizes,respectively, 0.63 and 1.25mm ofthe granular class); and
(3) propose a new method fordetermining the water absorptioncoefficient of the finer fraction ofFRCA.
This study is based on laboratory-made FRCA produced from threeconcretes that have been prepared in thelaboratory with two water–cement ratios(W/C) and two paste volumes. As aconsequence, the original concrete com-position was known and also FRCA werenot subjected to weathering duringstorage.
2. Materials and methods
2.1. Materials
Three original concretes with two differ-ent W/C ratios and volumes of paste
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were designed and manufactured forproduction of FRCA. Table 1 shows thedetails of original concrete compositions.OC1 and OC2 had the same W/C ratioand OC2 and OC3 had the same volumeof cement paste. The cement used in thisstudy was a white OPC (CEM I 52.5“superblanc”) provided by Lafarge com-pany whose mineralogical composition isshown in Table 2. Crushed calcareoussand and calcareous coarse aggregatessourced from Tournai (provided byHolcim France Benelux) were used forproduction of all original concretes. After28 (RCA-28) and 90 (RCA-90) dayscuring in water, original concretes havebeen crushed in the laboratory by using ajaw crusher with the same opening size(10mm). After crushing, RCA have beendried in the oven at 105 °C. The cumu-lated and partial particle size distributions(PSD) of all the crushed RCA are givenin Figures 1 and 2. These figures showthat, with the same jaw crusher opening,very similar PSD can be obtained for allthe concretes produced in the laboratory,whatever their properties and composi-
tions. Nevertheless, RCA-90 for the threeconcretes were coarser than RCA-28. Allthe crushed RCA have been separatedinto CRCA and FRCA. In this study, wefocus on the properties of FRCA(0/5mm). FRCA have then been sepa-rated by sieving in four different granularclasses (0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5mm) in order to study the influence ofgranular class on the properties of recy-cled aggregates. In the following, eachgranular class is represented by its aver-age particle size, corresponding to theaverage value of the minimal and maxi-mal particle sizes of the granular class.Each class has been tested for CPC,water absorption, density, porosity, andbound water content.
2.2. Experimental methods
2.2.1. Cement paste content
A method based on salicylic aciddissolution has been developed for thecharacterization of CPC in FRCA.Salicylic acid has been chosen because itallows the dissolution of most phases
Table 1. Original concrete compositions made in the laboratory (1 m3).
Type of original concrete OC1 OC2 OC3
Aggregate (kg) 1138.3 1040.7 1018.9Sand (kg) 756.4 691.5 677.0Cement (kg) 298.8 375.7 474.8Efficient water(kg) 179.3 225.4 189.9Absorbed water(kg) 17.2 15.7 15.4Total water(kg) 196.5 241.1 205.3Coarse aggregate/sand 1.505 1.505 1.505W/C ratio 0.6 0.6 0.4Volume of cement paste (dm3) 278 350 347Density of fresh concrete(kg/m3) 2390 2349 2376Slump (cm) 5.8 20.3 5.6fc28 (MPa) 41.1 40.8 51.0fc90(MPa) 47.3 46.4 57.6
Table 2. Mineralogical composition of cement determined by XRD-rietveld.
C3S C2S C3A C4AF Anhydrite Calcite Periclase
CEM I 52.5 superblanc (%) 73.90 21.87 1.46 – 0.52 1.53 0.72
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contained in OPC cement paste but notof the main phases contained in NA andespecially limestone (Table 3).[22–26]Three samples of each granular class ofFRCA have been measured to obtain anaverage value of the CPC.
The experimental protocol used is asfollows:
(1) a representative sample has beendried at 105 °C, then grinded untilpassing 0.2mm sieve;
Figure 1. Cumulated PSD of crushed RCA.
Figure 2. Partial PSD of crushed RCA.
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(2) 0.5 g of dried representative samplehas been immersed in a solution of14 g of salicylic acid in 80ml ofmethanol, and stirred for 1 h;
(3) the solid fraction has been filteredon glass filter (Pyrex No. 4, pores:10–16 μm) and washed four timesusing methanol (2–3mm high ontop of filter);
(4) the solid residue has been dried inthe oven at 70 °C for 30min; and
(5) the CPC is then calculated asfollows:
CPCð%Þ ¼ M1 �M2
M1� 100 ð1Þ
where M1 is the mass of dried materialbefore dissolution and M2 is the mass ofdried filtrate.
In order to validate this method,preliminary tests have been carried outwith NA and a pure cement paste havinga W/C ratio of 0.5. The cement pastewas manufactured with the same whitecement CEM I 52.5 “Superblanc” usedfor the rest of the study. Two kinds ofNA were used: a crushed calcareousaggregate from Tournai (the same as that
used for the production of concretesOC1, OC2 and OC3) and a siliceoussand complying with standard EN 196-1[27]. Table 4 presents the results afterdissolution. As can be seen, 95.6% of thecement paste was dissolved while only0.83% of siliceous aggregate and 3.21%of calcareous aggregates were dissolved.A small deviation is observed for allmaterials that confirms the robustness ofthe method.
2.2.2. Bound water content
A thermal method has been used to deter-mine the bound water content at 600 °Cof the cement paste in FRCA. Three sam-ples of each granular class of FRCA havebeen measured to obtain the averagevalue. The experimental protocol used isas follows:
(1) representative samples have beengrinded until passing 0.2mmsieve;
(2) the grinded representative sampleshave been pre-dried in the oven at105 °C until constant mass(1 day);
(3) dried samples were put in theoven at 600 °C until constant mass(1 day);
(4) the bound water content is calcu-lated from the mass differencebetween 105 and 600 °C.
In order to validate this method,thermogravimetric analysis (TGA) ofcement paste, calcareous sand, siliceousmortar, and calcareous mortar have beencarried out (Figure 3). This figure shows
Table 3. Insoluble and soluble phases insalicylic acid and methanol.
Insoluble phasesSolublephases
C3A, C4AF C2S, C3SQuartz, Dolomite CaO, Ca
(OH)2Calcite (limestone) C–S–HC3AH6, calcium
monosulfoaluminate hydrateEttringite
Table 4. Results of preliminary tests with salicylic acid dissolution-1 h (mass dissolved %).
Test 1 Test 2 Test 3 Average value Standard deviation value
Cement paste 95.46 96.35 94.89 95.57 0.74Siliceous sand 0.76 0.86 0.88 0.83 0.06Calcareous sand 3.42 3.03 3.18 3.21 0.20
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that calcareous sand and mortar decar-bonize over 600 °C whereas most of thepure cement paste is dehydrated below600 °C. Indeed, several authors [28–30]have shown that the dehydration ofC–S–H is about 180–300 °C and thedehydration of CH (Portlandite) is about450–550 °C. Therefore, a heating at600 °C has been chosen for the measure-ment of bound water content as it allowsavoiding the decarbonation of aggregates.The mass loss at 600 °C comes only fromthe dehydration of cement paste hydrates,and not from aggregates, it is, therefore,a good indicator of the CPC in thematerial.
2.2.3. Water absorption
The water absorption coefficient of eachgranular class of the FRCA has beenmeasured with two different methods: theEuropean standard method EN 1097-6[31] and the method no. 78 of IFSTTAR.[32] Three samples of each granular classof FRCA have been measured to obtainthe average value.
The principle of these methods issimilar: in both cases, samples are satu-rated for 24 h in water and then the waterabsorption coefficient is determined basedon the water content at saturated surfacedry (SSD) state. However, the dryingmethod and the way to identify the SSDstate are totally different. In the standardmethod (EN 1097-6), saturated aggre-gates are exposed to a gentle current ofwarm air to evaporate surface moistureand to reach the SSD state. The latter isidentified using a slump test on thedrying sample, which allows detectingthe existence of cohesion forces due tosurface moisture. A metal cone mould isfilled with the drying sample and liftedgently to let the aggregate flow under theeffect of gravity. The shape of the aggre-gate cone obtained after lifting allowsidentifying the SSD state (Figure 4). Inthe IFSTTAR method, the aggregates aredried progressively with different sheetsof colored absorbent paper until no traceof water can be seen on the paper (thesurface of each sheet of colored absor-bent paper was wiped carefully with a
Figure 3. TGA results obtained on cement paste, calcareous sand, siliceous mortar, andcalcareous mortar.
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brush to ensure that no fine particlesremain attached on the paper). In thatstate (SSD state), no moisture remains atthe surface of particles (third sheet ofpaper on Figure 5).
2.2.4. Density
For each RCA and each granular class,representative samples have been pre-dried in the oven at a temperature of
105 °C, and then specific density hasbeen measured by using helium pycnom-eter (Micromeritics AccuPyc 1330).
2.2.5. BET specific surface area andBJH porosity
The specific surface area of each granularclass of each FRCA has been measuredby using Brunauer–Emmett–Teller (BET)analysis using N2 adsorption (Micromeri-tics ASAP 2010). Representative sampleshave been pre-dried in the oven at a tem-perature of 105 °C and then cooled downin desiccators to room temperature. Thesesamples have then been used in the BETanalysis. Barrett–Joyner–Halenda (BJH)analysis has been employed to determinepore area and specific pore volume ondesorption isotherms.[33]
3. Results and discussion
3.1. Cement paste content
Figure 6 presents the variation of CPC asa function of granular class for all theFRCA studied. As can be seen inFigure 6, CPC is higher as the averageparticle size decreases. A reasonablelinear relation between CPC and granularclass is obtained. The correlation
Figure 4. Shape of cone corresponding to the SSD state (EN 1097-6 method).
Figure 5. Trace of water after successivedryings with absorbent paper (IFSTTARmethod).
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coefficients obtained (R²) range from0.8189 to 0.9985. For all the FRCA, thelarger values obtained for RCA-90 com-paratively to RCA-28 can be attributed tothe longer curing time in water. Thelonger the curing in the water, the higherdegree of hydration of cement paste, andthen the higher the CPC in the parentconcrete. Indeed, the mass of hydratedcement paste is higher than the mass ofinitial anhydrous cement, because anadditional quantity of water is added tothe initial anhydrous cement duringhydration. The larger values obtained forRCA-OC2 comparatively to RCA-OC1can be attributed to the higher volume ofcement paste in the original composition.Similarly, the larger values obtained forRCA-OC3 comparatively to RCA-OC2can be attributed to a lower W/C ratio inthe original composition, leading to adenser cement paste and, therefore, to alarger mass of cement paste for a similarpaste volume. Therefore, the CPC ofFRCA is influenced by the W/C ratio andthe cement paste volume of the originalconcrete.
Bound water content is connectedwith the degree of hydration and CPC.
Figure 7 shows the bound water contentof FRCA as a function of granular class.As can be seen, the bound water contentincreases as the average particle sizedecreases for all FRCA. A reasonable lin-ear relation between bound water contentand granular class is obtained, whichconfirms that the CPC varies quasi line-arly with the four granular classes thatwere used.
3.2. Water absorption
Figures 8 and 9 show the variation ofwater absorption coefficient of RCA-28and RCA-90 measured with the twomethods (EN1097-6 and IFSTTAR).The results obtained for RCA-OC1 andRCA-OC3 are very similar, whatever thegranular class. On the contrary, the waterabsorption coefficients obtained with allthe granular classes of RCA-OC2 aresignificantly larger than those obtainedwith RCA-OC1 and RCA-OC3. Thelarger values obtained for RCA-OC2comparatively to RCA-OC1 can be attrib-uted to the higher volume of cementpaste in the original composition. Simi-larly, the larger values obtained for
Figure 6. CPC as a function of the average size of the four different granular classes considered(0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5mm).
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RCA-OC2 comparatively to RCA-OC3can be linked to a larger W/C ratio in theoriginal composition, leading to a greaterporosity of the cement paste.
The results obtained with the twoexperimental methods (EN1097-6 andIFSTTAR) were very close from one toanother except for the smaller fraction(0/0.63mm). For all FRCA tested in ourstudy, the water absorption coefficientincreased when the average particle size
decreased except for the fraction0/0.63mm with the standard EN1097-6.For the smaller fraction, the standardmethod does not allow to identifyprecisely the SSD state. Indeed, for verysmall angular particles (like thoseobtained from crushed concrete), the sandcan present some cohesion even if all thewater at the surface of particles has beenremoved, preventing the sand cone tocollapse [34]. The standard method,
Figure 7. Bound water content as a function of the average size of the four different granularclasses considered (0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5mm).
Figure 8. Water absorption of RCA-OC-28 measured by EN1097-6 and IFSTTAR methods as afunction of the average size of the four different granular classes considered (0/0.63, 0.63/1.25,1.25/2.5, 2.5/5mm).
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therefore, underestimates the waterabsorption coefficient for small particles.On the contrary, with IFSTTAR method,the water absorption coefficient increasesa lot for the smaller fraction. Figure 10presents an optical microscopy image ofthe fraction 0–0.63mm of RCA-OC1-28at SSD state with IFSTTAR method. Ascan be seen, agglomerates larger than2mm (much larger than the maximum
particle size of 0.63mm) are present.This result is due to the fact that verysmall particles tend to agglomerate duringdrying because of capillary forces. Absor-bent paper allows drying the surface ofthese agglomerates, but the method useddoes not allow breaking them. IFSTTARmethod, therefore, overestimates thewater absorption coefficient of the finerfraction.
Figure 9. Water absorption of RCA-OC-90 measured by EN1097-6 and IFSTTAR methods as afunction of the average size of the four different granular classes considered (0/0.63, 0.63/1.25,1.25/2.5, 2.5/5mm).
Figure 10. Optical microscopy of fraction 0–0.63mm of RCA-OC1-28 at SSD state by theIFSTTAR method.
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3.3. Density and porosity
Figure 11 presents the variation ofdensity measured with the heliumpycnometer as a function of granularclass. The density of all the fractions ofFRCA is lower than that of NA(2.67 g/cm3). This is due to the cementpaste surrounding NA, whose density issmaller than that of natural calcareousaggregates. Figure 11 also shows that thedensity of FRCA increases as the averageparticle size increases.
Figure 12 shows the BJH porosity ofall the granular classes of FRCA. Theporosity of FRCA increases as the
average particle size of FRCA decreases.The larger values obtained for RCA-OC2comparatively to RCA-OC1 can be attrib-uted to the higher volume of cementpaste in the original composition of OC2(same W/C ratio). Similarly, the largervalues obtained for RCA-OC2 compara-tively to RCA-OC3 can be attributed to alarger W/C ratio in the original composi-tion of OC2 (same volume of cementpaste), leading to a larger porosity of thecement paste. So, as expected, the poros-ity of FRCA is influenced by the W/Cratio and the cement paste volume of theoriginal concrete. Generally, the porosity
Figure 11. Density of FRCA as a function of the average size of the four different granularclasses considered (0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5mm).
Figure 12. BJH porosity of FRCA as function of the average size of the four different granularclasses considered (0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5mm).
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of RCA-90 is lower than RCA-28 whichis due to higher hydration degree ofcement paste (except for the fractions0.63–1.25 and 2.5–5 for RCA-OC1 andfor the fraction 2.5–5 for RCA–OC2).
3.4. Relationships between CPC andthe other studied properties
Figure 13 shows the variation of boundwater content as a function of CPC. Fora given original concrete compositionand a given hydration degree, the boundwater content increases linearly with theCPC (R² ranges from 0.867 to 0.9978).Table 5 shows that the slope of boundwater to cement paste is similar forRCA-OC1 and RCA-OC2, and the slopeof RCA-OC 90 is higher than RCA-OC28. Indeed, the mass dissolved insalicylic acid and the mass loss at 600 °Cboth depend closely on the cement pasteproportion in the material. However,salicylic acid leads to the dissolution ofboth anhydrous phases (except C4AF)and hydrates whereas heating at 600 °Conly leads to the decomposition ofhydrates but does not affect the anhy-drous phases. Therefore, when comparingtwo cement pastes having different hydra-tion degrees like in Figure 13, the mass
loss at 600 °C will be larger for thecement paste having the larger hydrationdegree. Indeed, for a given CPC (mea-sured by the mass dissolved in salicylicacid), the paste with the larger hydrationdegree contains more hydrates than theone with the lower hydration degree.
Figure 14 shows the variation ofspecific density as a function of CPC.When CPC increases, specific densitydecreases linearly. The density of RCAdirectly depends on density of cementpaste and of NA and on the proportion ofcement paste. For a given RCA, if ρNA isthe density of NA and ρCP is the densityof cement paste, then the density of agiven granular fraction of RCA (ρRCA)can be calculated with Equation (2):
Figure 13. Bound water vs. CPC.
Table 5. Coefficients of the linearrelationships between bound water contentand CPC (y = ax + b).
a b R2
RCA-OC1-28 0.1134 3.684 0.867RCA-OC2-28 0.1265 3.0191 0.9448RCA-OC3-28 0.1722 1.3674 0.9978RCA-OC1-90 0.1699 3.3695 0.9262RCA-OC2-90 0.1895 3.1609 0.9919RCA-OC3-90 0.3246 �1.0356 0.9688RCA-OC-28 0.1025 3.77 0.8573RCA-OC-90 0.2387 1.741 0.9516
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qRCA ¼ qNA
1þ CPC � qNA�qCPqCP
ð2Þ
where CPC is the CPC of the consideredgranular fraction.
The density of each cement paste canthen be obtained by fitting Equation (2)with our experimental results (Table 6).Table 6 shows that the densities ofcement paste in RCA-OC1-28 and RCA-OC2-28 (similarly for RCA-OC1-90 andRCA-OC2-90) are similar as expected.Indeed, cement paste of RCA-OC1 andRCA-OC2 have the same W/C ratio.Moreover, the larger values obtained forRCA-OC3 comparatively to RCA-OC1and RCA-OC2 can be attributed to thelower W/C in the original composition.As the hydration degree of originalconcrete increases (from RCA-28 toRCA-90), the density of cement pasteincreases. Table 6 also shows that thecorrelation coefficients obtained betweencalculated and experimental value (R²)range from 0.9230 to 0.9926.
Figure 15 presents the variation ofwater absorption (IFSTTAR method) withthe CPC: when CPC increases, the waterabsorption increases too. As can be seen,the water absorption of all FRCA varieslinearly with the CPC for the three coar-ser average particle sizes of RCA. On thecontrary, as discussed previously, thewater absorption measured by standard orIFSTTAR method for the finer fractionseems to be either underestimated oroverestimated, respectively (example forRCA-OC3-90 shown on Figure 15). Thewater absorption of RCA directlydepends on the water absorptions ofcement paste and of NA and on the pro-portions of cement paste. For a given ori-ginal concrete composition, the waterabsorption coefficients of NA (WANA)and of the cement paste (WACP) do notdepend on the granular fraction consid-ered. Therefore, the water absorption of agiven granular fraction of RCA (WARCA)can be calculated with Equation (3) (seeTable 7).
Figure 14. Correlation between cement paste and specific density.
Table 6. Density of cement paste calculated by the correlation between density and cementpaste Equation (2).
RCA-OC1-28 RCA-OC2-28 RCA-OC3-28 RCA-OC1-90 RCA-OC2-90 RCA-OC3-90
Density 2.002 1.962 2.068 2.035 2.038 2.095R2 0.9533 0.9230 0.9728 0.9805 0.9615 0.9926
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WARCA ¼ WACP � CPCþWANA
� ð1� CPCÞ ð3Þ
where CPC is the CPC of the consideredgranular fraction.
Equation (3) shows that the waterabsorption coefficient of RCA has to varylinearly with the CPC. Therefore, thewater absorption coefficient of the finerfraction (0/0.63mm) can be obtained bylinear extrapolation of the relationbetween WA and CPC determined withthe three coarser fractions of RCA.Extrapolation carried out using both
standard and IFSTTAR methods givessimilar values for the water absorptioncoefficient of the finer fraction (Table 8);the average difference between these twovalues obtained for the six FRCA is1.06%. As expected, the value of waterabsorption coefficient of finer fractionobtained is between the value obtainedby the standard and IFSTTAR methods.In Figure 15, the water absorption coeffi-cients of the smaller granular classes (0–0.63mm) correspond to the extrapolatedvalues from experimental results withIFSTATAR method. The values obtainedby the standard and IFSTTAR methodsare also reported for RCA-OC3-90 todemonstrate that these values are notappropriate.
Therefore, we propose the followingmethod to estimate the water absorptioncoefficient of the finer fraction (0–0.63mm) of FRCA. FRCA first have tobe separated in different granular classes.In our study, the four classes, 0/0.63,0.63/1.25, 1.25/2.5, 2.5/5mm, have beenretained because they allowed separatingthe FRCA into classes representing sig-nificant proportions of the aggregate.
Figure 15. Correlation between water absorption (IFSTTAR method) and CPC.
Table 7. Coefficients of the linearrelationships between water absorption(IFSTAAR method for three coarse fractions)and CPC (y= ax+ b).
a b R2
RCA-OC1-28 0.5567 �3.0928 0.9318RCA-OC2-28 0.6408 �5.51 0.9829RCA-OC3-28 0.433 �4.6383 0.991RCA-OC1-90 0.3825 0.235 0.8265RCA-OC2-90 0.4581 �3.0639 0.9925RCA-OC3-90 0.3775 �3.5786 0.9801
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However, depending on the particle sizedistribution of the FRCA, different granu-lar classes could be chosen. First, theCPC of each granular class have to bedetermined using the salicylic acid disso-lution method described in this paper.Then, the water absorption coefficients ofthe three coarser fractions of FRCA haveto be measured either with Europeanstandard EN 1097-6 or IFSTTAR methodno. 78. Finally, the water absorption coef-ficient of the finer fraction (0/0.63mm)can be obtained by a linear extrapolationbetween WA and CPC of the threecoarser classes. The accurate total waterabsorption of FRCA used (fraction0/5mm) can be determined by knowingthe proportion and water absorption coef-ficient of each fraction.
Additionally, drawing the waterabsorption coefficient as a function of theCPC can be a very convenient method todifferentiate different sources of RCA forwhich the original concrete compositionis generally unknown. Changes of theslope of this regression can also be usedto estimate the effect of the weathering orsome specific treatment after RCA beingcrushed. Indeed, for a given RCA, thepresence of insoluble phases of thecement paste (Table 3) will impact simi-larly all the four particle size classes.Thus, the linear relationship between theCPC and the average size of the fourdifferent granular classes will be kept. Onthe other hand, insoluble phases willimpact the coefficients of the linear
regression of the water absorption coeffi-cient as a function of CPC as this latterwill decrease with an increase of the con-tent of insoluble phases.
4. Conclusions
Some of the major properties of FRCAproduced in the laboratory from thecrushing of concretes of known composi-tion have been related to the CPC. Amethod based on the dissolution of themajor part of the cement paste containedin FRCA by salicylic acid has beendeveloped for the measurement of CPC.The method was applied to concrete man-ufactured with a white OPC to obtain themost reliable results. However, it can beapplied to grey OPC as the presence ofinsoluble phases of the cement paste willimpact similarly all the particle sizeclasses.
Main conclusions obtained are as fol-lows:
(1) For the FRCA used in this study,the CPC decreases linearly withthe average particle size of fourdifferent granular classes (0/0.63,0.63/1.25, 1.25/2.5, 2.5/5mm).This result has been confirmed bystudying the variation of boundwater content of FRCA (mass lossat 600 °C) as a function ofaverage particle size. However,different relations could beobtained between CPC and parti-
Table 8. Extrapolated water absorption coefficient of Fraction 0–0.63mm from standard andIFSTTAR.
Tested valueof IFSTTAR
(%)
Tested valueof EN 1097-6
(%)
Extrapolatedvalue of
IFSTTAR (%)
Extrapolatedvalue of EN1097-6 (%)
Difference of twoextrapolatedvalues (%)
RCA-OC1-28 21.9 7.61 11.68 10.50 1.19RCA-OC2-28 23.18 8.05 15.42 15.87 �0.45RCA-OC3-28 21.44 9.74 11.52 10.43 1.09RCA-OC1-90 17.66 9.42 10.67 9.82 0.85RCA-OC2-90 22.84 9.77 14.81 13.67 1.14RCA-OC3-90 16.79 6.52 10.90 9.28 1.62
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cle size for other types of RCA. Astudy performed on industrialRCA of various origins is in pro-gress.
(2) The properties of FRCA includingspecific density, water absorption,and porosity are strongly correlatedto the CPC. The higher the CPC,the higher the water absorption andporosity, and the lower the specificdensity at the exception of theabsorption coefficient measured byEN 1097-6 standard for the smallerfraction (0/0.63mm).
(3) For particle sizes larger than0.63mm, EN 1097-6 and IFST-TAR methods gave similar results,which suggest that these methodsare relevant for the measurementof water absorption coefficient ofFRCA (larger than 0.63mm). Forthese fractions, a linear relation isfound between the water absorp-tion coefficient and the particlesize; the former decreasing withthe latter. However, for the smallerparticle size (<0.63mm), IFST-TAR method seems to overesti-mate the water absorptioncoefficient, and standard method(EN 1097-6) seems to underesti-mate it. The characterization ofwater absorption coefficient ofvery fine particles is known to bea difficult task, especially forFRCA. As the water absorptiondisplays a linear relationship withCPC of the three coarser granularclasses, the absorption coefficientcould be estimated with goodaccuracy for very fine RCA byextrapolating the relationshipobtained between water absorptionand CPC with coarser granularclass. The total water absorptionof FRCA (fraction 0/5mm) can,therefore, be determined preciselywhich is very important in the
mixture proportioning of recycledconcrete.
(4) The water absorption coefficientsof the FRCA studied rangebetween 6.7 and 15.9%, which ismuch larger than the waterabsorption coefficient of commonNA. The presence of cementpaste, much more porous than theNA used, is responsible for theselarge absorption values.
AcknowledgmentsAuthors would like to thank the LafargeCompany for its cement and the HolcimCompany for supplying natural aggregates.Authors would also like to thank the ColasCompany for supplying materials. Finally,authors would like to thank the ChinaScholarship Council (CSC) for its financialsupport.
References[1] Kou S-C, Poon C-S. Effects of different
kinds of recycled fine aggregate on prop-erties of rendering mortar. Journal ofSustainable Cement-Based Materials.2013;2:43–57.
[2] Poon C-S, Chan D. The use of recycledaggregate in concrete in Hong Kong.Resources, Conservation and Recycling.2007;50:293–305.
[3] Rao A, Jha KN, Misra S. Use of aggre-gates from recycled construction anddemolition waste in concrete. Resources,Conservation and Recycling. 2007;50:71–1.
[4] Shi J, Xu Y. Estimation and forecastingof concrete debris amount in China.Resources, Conservation and Recycling.2006;49:147–58.
[5] Angulo S, Mueller A. Determination ofconstruction and demolition recycledaggregates composition, in consideringtheir heterogeneity. Materials and Struc-tures. 2009;42:739–48.
[6] Hansen TC. Recycled aggregates andrecycled aggregate concrete second state-of-the-art report developments 1945–1985. Materials and Structures. 1986;19:201–46.
[7] Tam VWY, Tam C. Parameters forassessing recycled aggregate and theircorrelation. Waste Management andResearch. 2009;27:52–58.
16 Z. Zhao et al.
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ded
by [
Eco
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es M
ines
de
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ai]
at 0
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16
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ust 2
013
[8] Domingo A, Lázaro C, Gayarre F, Ser-rano M, López-Colina C. Long termdeformations by creep and shrinkage inrecycled aggregate concrete. Materialsand Structures. 2010;43:1147–160.
[9] Hansen TC, Boegh E. Elasticity and dry-ing shrinkage of recycled-aggregate con-crete. Journal of the American ConcreteInstitute. 1985;82:648–652.
[10] Hansen TC, Narud H. Strength ofrecycled concrete made from crushedconcrete coarse aggregate. ConcreteInternational. 1983;5:79–83.
[11] Etxeberria M, Vázquez E, Marí A, BarraM. Influence of amount of recycledcoarse aggregates and production processon properties of recycled aggregate con-crete. Cement and Concrete Research.2007;37:735–42.
[12] Evangelista L, de Brito J. Mechanicalbehaviour of concrete made with finerecycled concrete aggregates. Cement andConcrete Composites. 2007;29: 397–401.
[13] Khatib JMK. Properties of concrete incor-porating fine recycled aggregate. Cementand Concrete Research. 2005;35: 763–69.
[14] Kou S-C, Poon C-S. Properties of con-crete prepared with crushed fine stone,furnace bottom ash and fine recycledaggregate as fine aggregates. Constructionand Building Materials. 2009;23:2877–886.
[15] Hu J, Wang Z, Kim Y. Feasibility studyof using fine recycled concrete aggregatein producing self-consolidation concrete.Journal of Sustainable Cement-BasedMaterials. 2013;2:20–34.
[16] Tam VWY, Wang K, Tam CM. Assess-ing relationships among properties ofdemolished concrete, recycled aggregateand recycled aggregate concrete usingregression analysis. Journal of HazardousMaterials. 2008;152:703–14.
[17] de Juan MS, Gutiérrez PA. Study on theinfluence of attached mortar content onthe properties of recycled concrete aggre-gate. Construction and Building Materi-als. 2009;23:872–77.
[18] Nagataki S, Gokce A, Saeki T, HisadaM. Assessment of recycling processinduced damage sensitivity of recycledconcrete aggregates. Cement andConcrete Research. 2004;34:965–71.
[19] Abbas A, Fathifazl G, Fournier B, IsgorOB, Zavadil R, Razaqpur AG, et al.Quantification of the residual mortar con-
tent in recycled concrete aggregates byimage analysis. Materials Characteriza-tion. 2009;60:716–28.
[20] Tam VWY, Gao XF, Tam CM, ChanCH. New approach in measuring waterabsorption of recycled aggregates. Con-struction and Building Materials.2008;22:364–69.
[21] Tegguer A. Determining the waterabsorption of recycled aggregates utiliz-ing hydrostatic weighing approach. Con-struction and Building Materials.2012;27:112–16.
[22] Gutteridge WA. On the dissolution of theinterstitial phases in Portland cement.Cement and Concrete Research.1979;9:319–24.
[23] Ohsawa S, Asaga K, Goto S, DaimonM. Quantitative determination of flyash in the hydrated fly ash –CaSO4·2H2O–Ca(OH)2 system. Cementand Concrete Research.1985;15:357–66.
[24] Luke K, Glasser FP. Selective dissolutionof hydrated blast furnace slag cements.Cement and Concrete Research.1987;17:273–82.
[25] Le Saout G, Lécolier E, Rivereau A,Zanni H. Chemical structure of cementaged at normal and elevated temperaturesand pressures: part I. Class G oilwellcement. Cement and Concrete Research.2006;36:71–78.
[26] Lothenbach B, Le Saout G, Ben HahaM, Figi R, Wieland E. Hydration of alow-alkali CEM III/B–SiO2 cement(LAC). Cement and Concrete Research.2012;42:410–23.
[27] NF EN 196-1: 2005(E). Methods of test-ing cement - Part 1: Determination ofstrength. Brussels: European Committeefor Standardization.
[28] DeJong MJ, Ulm F-J. The nanogranularbehavior of C–S–H at elevated tempera-tures (up to 700 °C). Cement and Con-crete Research. 2007;37:1–12.
[29] Kojima Y, Numazawa M, Umegaki T.Fluorescent properties of a blue-togreen-emitting Ce3+, Tb3+ codopedamorphous calcium silicate phosphors.J. Luminescence. 2012;132:2992–996.
[30] Alarcon-Ruiz L, Platret G, Massieu E,Ehrlacher A. The use of thermal analysisin assessing the effect of temperature ona cement paste. Cement and ConcreteResearch. 2005;35:609–13.
Journal of Sustainable Cement-Based Materials 17
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[31] NF EN 1097-6:2000. Tests for mechani-cal and physical properties of aggregates- Part 6: Determination of particle den-sity and water absorption. Brussels:European Committee for Standardization.
[32] IFSTTAR. Test Method No. 78:2011.Tests on aggregates for concrete: mea-surement of total water absorption by acrushed sand. Paris: IFSTTAR.
[33] Brunauer S, Emmett PH, Teller E.Adsorption of gases in multimolecularlayers. Journal of the American ChemicalSociety. 1938;60:309–19.
[34] ASTM C 128–04: 2004. Standard testmethod for density, relative density (spe-cific gravity), and absorption of fineaggregate. West Conshohocken, PA:ASTM International.
18 Z. Zhao et al.
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