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7KLVSDSHUSUHVHQWVDODERUDWRU\VWXG\ZLWKWKHPDLQSXUSRVHRIYHULI\LQJWKHSRWHQWLDOLQFDXVLQJDONDOLVLOLFDDQGDONDOL carbonate reactivity of dolomite rock. With this approach, several methodologies in the ASR and ACR investigations and a detailed mineralogical analysis of the mentioned rocks are showed and the tested results discussed.
7KHUHVXOWVLQGLFDWHWKDWDONDOLVLOLFDUHDFWLRQGRHVQRWRFFXULQQRQVLOLFHRXVFDUERQDWHDJJUHJDWHHYHQZLWKDYHU\ORZ content of SiO2.
Keywords: alkali-aggregate reaction (AAR), ACR
1. Introduction
Alkali-aggregate reaction (AAR) can occur in concrete in some conditions causing damage due WR W\SLFDOO\ H[SDQVLRQ RI DJJUHJDWH 7KH DONDOL aggregate reaction is a chemical process in which some components of the aggregate react with dissolved DONDOLQHK\GUR[LGHVLQFRQFUHWHVROXWLRQ7KHUHDFWLRQ is divided into three types: alkali-silica reaction (ASR), alkali-silicate reaction and alkali-carbonate reaction (ACR), depending on the mineralogy of the rock. ASR is related mainly to opal, trydimite, crystobalite and YROFDQLFJODVV>@ DONDOLVLOLFDWHUHDFWLRQZKLFKLVD VSHFL¿FW\SHRI$65EXWGHYHORSVDWDORZUDWHZKHQ compared to ASR, involves strained quartz and some SK\OORVROLFDWHPLQHUDOV>@ WKHWKLUGW\SHRI$$5WKDW is ACR is attributed to the presence of dolomite from FDOFLWLFGRORPLWHVDQGGRORPLWLFOLPHVWRQH>@
The mechanism of alkali-carbonate reaction is still unclear. It is agreed that there are three key elements causing the alkali-reaction of carbonate aggregate: crystal grains of dolomite distributed in the
FRQWLQXRXVFOD\LVKQHWZRUN
the dimension of the crystal grains, they are rhombohedron idiomorphic crystal of dolomite, ZKLFK VKRXOG EH VPDOOHU WKDQ ȝP DQG WKH DO7\VLłFOHFLD3DŐVWZD3ROVNLHJR
.LHOFH3RODQG HPDLO RZVLDN#WXNLHOFHSO
INVESTIGATION OF ALKALI-AGGREGATE
REACTION IN CARBONATE ROCKS
higher alkali reactivity the less the dimension. If the dimensions of the crystal grains are bigger than ȝPWKHQWKHDONDOLUHDFWLRQRIWKHFU\VWDOJUDLQV FDQQRWFDXVHWKHGHWHUPLQDWLRQRIWKHFRQFUHWH the content of clay, which made the continuous
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For the mechanism of alkali-carbonate reaction in carbonate aggregate, three hypotheses have been SURSRVHG 7KH ¿UVW LV GHGRORPLWL]DWLRQ K\SRWKHVHV ,Q ¶V':+DGOH\>@SURSRVHGWKDWWKHUHDFWLYH FDUERQDWH DJJUHJDWH UHDFWHG ZLWK WKH SRUH ÀXLG LQ the concrete. That causes dedolomitization and the IRUPDWLRQRIEUXFLWHDQGWKHH[SDQVLRQ7KHVHFRQG K\SRWKHVHVLVWKDWWKHH[SDQVLRQLVFDXVHGE\WKHZDWHU absorption by dry clay. It was proposed by Swenson and *LOORWW>@7KH\WKRXJKWWKDWWKHGU\FOD\H[SRVHGDVD result of dedolomitization, and provided the alleyway ZKLFKWKHZDWHUFDQSDVV1H[WWKHVXUIDFHRIWKHFOD\ absorbs the water and forms the electrical double layer structure. The water absorption by dry clay causes H[SDQVLRQ7KLVLVWKHPDLQUHDVRQIRUWKHH[SDQVLRQ caused by the alkali-carbonate reaction. The third is the synthetical action. This mechanism was proposed E\07DQJLQ > @+HWKRXJKWWKDWWKHH[SDQVLRQ was caused by topochemical reaction resulting from
the entry of K+, Na+, and OH- into the restricted space.
7KDW FDXVHV FRQVLGHUDEOH H[SDQVLYH SUHVVXUH 7KH ZDWHUDEVRUEHGE\GU\FOD\FDXVHH[SDQVLYHSUHVVXUH the pressure of crystallization of brucite and calcite, and the osmotic pressure caused by difference ion concentration from the liquid after reaction to the pore space in hardened cement. However, these views are contradictory and more research is still necessary. 2. Materials and methods
2.1. Materials
The dolomite aggregate of 2/16 mm fraction and 3RUWODQGFHPHQW&(0,ZHUHXVHGLQWKHWHVWV The physico-mechanical properties of the aggregate are presented in Table 1. Table 2 presents the chemical composition of cement.
Table 1. Physico-mechanical properties of the dolomite
aggregate
Test Results Method
Determination of the resistance to wear – micro ±'HYDOFRHI¿FLHQW0DE
9.70 PN-EN 1097–1: 2000; A1: 2004 Determination of the
resistance to fragmentation
±/RV$QJHOHVFRHI¿FLHQW/$ 19 PN-EN 1097–2: 2000; A1: 2008 /RRVHEXONGHQVLW\0JP3 1.46 PN-EN 1097– 3: 2000 $SSDUHQWSDUWLFOHGHQVLW\ 0JP3 2.84 PN-EN 1097–6: 2002; A1: 2006 3UHGULHGSDUWLFOHGHQVLW\ 0JP3 2.77 Particle density on a saturated and surface GULHGEDVLV0JP3
2.80 :DWHUDEVRUSWLRQ 0.87
7RWDOVXOIXUFRQWHQW 0.06 PN-EN 1744 – 1: 2000 p. 11
Table 2. The chemical composition of Portland cement
&(0,
L.O.I. SiO2 Fe2O3 Al2O3 TiO2 CaO 0J2 SO3 Na2O K2O Na2Oeq 2.45 21.50 4.00 4.25 0.07 63.5 0.60 2.45 0.28 0.55 0.65
2.2. Methods for rock assessment
The investigation methods were selected with the aim to verify the behaviour of carbonate rocks used as aggregate, as well as their reactions with the cement paste. The rocks were assessed in their natural state. They were investigated with several methods, described as follows.
7KH WH[WXUH PLQHUDORJLFDO DQG FKHPLFDO characterization of the selected carbonate rock were
evaluated through petrographic, mineralogical, diffractometric and chemical analyses.
,QDGGLWLRQWRWKHLQIRUPDWLRQRQWKH$670& [2] standard, the petrographic analysis was conducted in accordance with the conventional techniques of PLFURVFRSLF DQDO\VLV IRU GHWHUPLQDWLRQ RI WH[WXUH DQG composition characteristics of the rock. Microscopic petrographic analyses were performed using the transmitted light optic microscope. The aim was to classify the rock and estimate its mineralogy, mostly in what refers to carbonates and silicates. In this method, WKHFRQFHUQZDVWRSHUIRUPDUHSUHVHQWDWLYHVDPSOLQJ therefore, three impregnated thin sections were prepared.
,GHQWL¿FDWLRQ RI FU\VWDOOLQH SKDVH RI WKH FDUERQDWH aggregate rock was done through X-ray diffraction (XRD). This analysis was considered very useful as a complementary evaluation to the petrographic FODVVL¿FDWLRQRIWKHURFN7KHVDPSOHZDVVXEPLWWHG WRDSUHYLRXVJULQGLQJ ¿QHUWKDQȝP WRSURYLGH UHSUHVHQWDWLYH ¿QH VL]H PDWHULDO 7KLV PDWHULDO ZDV VXEPLWWHGWRSRZGHUGLIIUDFWLRQ[UD\DQDO\VLV LQWHJUDO sample).
The chemical analysis was performed according WRWKHFRPSOH[RPHWULFPHWKRGWRREWDLQ$O&DDQG 0J R[LGHV DQG JUDYLPHWULFDO PHWKRG WR GHWHUPLQH VLOLFHRXVR[LGHDQGLQVROXEOHUHVLGXH7KHREMHFWLYHRI this analysis was to quantify the chemical elements in the aggregate. Also, to correlate them to the potential reactivity of the rock, according to the chemical PHWKRG>@
For the investigation of ASR on carbonate rock, the accelerated mortar bar test according to the ASTM C – 1260 standard [6] was used. It was done by casting ¿YHPRUWDUEDUVZLWKVHOHFWHGURFNW\SHVDVDUWL¿FLDO ¿QH DJJUHJDWH FRQVLGHULQJ WKH FHPHQW DJJUHJDWH SURSRUWLRQ RI DQG ZF UDWLR 7KH EDUV ZHUHLPPHUVHGLQ1VRGLXPK\GUR[LGHVROXWLRQDW 80o&IRUGD\V7KHFHPHQWXVHGFRQWDLQHGDORZ
alkaline equivalent (Na2Oeq UHSUHVHQWLQJ RI total (acid soluble) alkalis, respectively.
3. Results
5RFNFKDUDFWHUL]DWLRQ
The tests involved dolomite aggregate. In macroscopic terms it had non-uniform microstructure. The results from the petrographic analyses are presented in Figure 1 and Figure 2. The microscope DQDO\VLVVKRZWKDWWKHDJJUHJDWHWH[WXUHLVFRPSDFW with visible pores in the form of druses with sharp HGJHVWKHWH[WXUHVRPHWLPHVEHLQJJUDQXODU )LJ
a)
b)
c)
d)
Fig. 1. The microstructure of the grains of compact WH[WXUHGRORPLWH D F G SDUDOOHOSRODULVHUVE FURVVHG
polarisers (colouring with alisarine, calcite grains have a red colour, dolomite grains are colourless) 7KHFRQWHQWRIJUDQXODUWH[WXUHGRORPLWHLVDERXW DQGWKHFRQWHQWRIFRPSDFWWH[WXUHGRORPLWHLV
DERXW 7KH DJJUHJDWH KDV ¿QH JUDLQ VWUXFWXUH and the colour range from light yellow to pink. The microscopic analysis (Fig. 1) have revealed that it is DFRPSDFWUDQGRPWH[WXUHGRORPLWHZLWKD¿QHJUDLQ VWUXFWXUH JUDLQVZLWKWKHPHDQVL]HIURPWR mm) mostly the equal-size grain structure, less often the different-size grain structure. At some places one may observe the traces of original structures (oval formations, sometimes with grains smaller than 0.001 mm). Calcite appears sporadically in the form of VLQJOHDXWRPRUSKLFJUDLQVZLWKWKHVL]HRIDERXW mm. Pores are rare and appear in the form of irregular FUDFNVRUGUXVHVZLWKWKHVL]HRIDERXWPP
)LJXUH VKRZV H[DPSOHV RI PLFURVFRSLF LPDJHV of dolomite and organogenic limestone grains with calcite as the binder. Grains with weakly marked concentric form have blurred oval outlines, the binder appears in the form of automorphic grains with the size of about 0.1 mm.
a)
b)
Fig. 2. The microstructure of organogenic dolomite grains with the calcite binder: a) crossed polarisers (colouring with alisarine, calcite grains have a red colour, dolomite
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 D C C C C C C C D D D D D D D D D D D D D C- kalcyt D - dolomit
The results from the XRD analyses of rock are SUHVHQWHGLQ)LJXUHWKH6(0PLFURJUDSKLQ)LJXUH DQGWKHFKHPLFDODQDO\VHVDUHSUHVHQWHGLQ7DEOH
)LJ6(0PLFURJUDSKRIGRORPLWH
Table 3. The composition of the aggregate
Component SiO2 Al2O3 Fe2O3 CaO 0J2 0Q2 K2O Na2O SO3 TiO2 &RQWHQWV 6.95 0.65 0.93 29.6 18.5 0.08 0.15 0.02 <0.01 0.02
The dolomite appears as the major component DERXW IROORZHG E\ WKH FDOFLWH DERXW Silicates occur in all analyzed rock in small (trace) quantities, mainly quartz, illite. Their presence is corroborated by the results from chemical analysis revealing minor contests of SiO2, Al2O, as well as insoluble residue. 3.2. Expansion test )LJXUHVKRZVWKHH[SDQVLRQUHVXOWVE\WKHDJHRI GD\VRIWKHFDUERQDWHURFNVDPSOHV -0,02 0 0,02 0,04 0,06 0,08 0,1 0,12 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Curing time [days]
Ex p a n s io n [ % ] CEM I )LJ7KHH[SDQVLRQUHVXOWVIURPWKHSHULRGRIGD\V RIWKHFDUERQDWHURFNVDPSOHV ZLWK$670& 7KHH[SDQVLRQRIWKHDJJUHJDWHUHDFKHGDW GD\V7KDWZDVORZHU WKDQWKHVSHFL¿HGQXPEHULQ $670&7KXVQRQVLOLFHRXVFDUERQDWHURFN even with a low content of SiO2, can be nonreactive with alkalis.
4. Discussion
$FFRUGLQJ WR $670 & ± H[SDQVLRQ XS WR LQ GD\V PHDQV UHDFWLYH EHKDYLRXU RI WKH DJJUHJDWH<HWIRUH[SDQVLRQEHORZDIWHUWKH same time, the aggregate is considered innocuous. The results reveal that the aggregate showed limited H[SDQVLRQ 7KXV WKH UHDFWLYLW\ RI WKH DJJUHJDWH LV ORZ7KHH[SDQVLRQLVQRWGXHWRWKHDONDOLDJJUHJDWH reaction.
The dolomite aggregate has good physical properties and meets the requirements for the concrete aggregates. Dolomite is the main component of the rock, which also includes small quantities of calcite, FOD\PLQHUDOVDQGTXDUW]7KHURFNKDVD¿QHJUDLQ structure and a colour range from light yellow to pink.
7KHFRQWHQWRIFRPSDFWWH[WXUHGRORPLWH LVDERXW DQGWKHFRQWHQWRIJUDQXODUWH[WXUHGRORPLWHLVDERXW &DOFLWHDSSHDUVUDQGRPO\LQWKHIRUPRIVLQJOH DXWRPRUSKLFJUDLQVZLWKWKHVL]HRIDERXWPP 6RPHWLPHVLURQR[LGHVDSSHDULQWKHURFNLQWKHIRUP RIRYDOFOXVWHUVZLWKWKHVL]HRIDERXWWR mm or as short veins. Pores are rare. They appear in the form of irregular cracks or druses with the size of DERXWPP7KHLQYHVWLJDWHGJUDLQVRIWKH¿QH grain micrite dolomite (the size of grains smaller than PP DUHERQGHGZLWKFRDUVHFU\VWDOOLQHFDOFLWH cement&DOFLWHZLWKWKHJUDLQVL]HRIDERXWPP and bigger appears in the veins and pervades the dolomite in the aggregate-paste interface. There are VPDOOTXDQWLWLHVRILURQR[LGHVDQGVSRUDGLFDOO\WKH grains of corroded quartz and microsilica. There also appear granular pieces of dolomite and organogenic limestone with calcite as a binder and dolomite or calcite grains.
5. Conclusions
Considering its mineral composition, the aggregate applied in this research could have been of the alkali-reactive type. From the analysis it is evident,
however, the aggregate is possibly not reactive with alkali. Neither the silica reaction nor the alkali-carbonate aggregate reaction were observed.
References
>@$670 & Standard Test Method for Determining the Potential Alkali Reactivity of Combinations of Cementious Materials and Aggregate $FFHOHUDWHG 0RUWDU %DU 0HWKRG . Annual Book of $6706WDQGDUGV
>@$670& Standard Guide for Petrographic Examination of Aggregate for Concrete.
>@&6$ $$ Determination of potential DONDOLFDUERQDWH UHDFWLYLW\ RI TXDUULHG FDUERQDWH rocks by chemical composition, Canadian Standards Association, CSA International, Canada.
>@*LOORWW-(Mechanism and Kinetics of Expansion in WKH $ONDOL&DUERQDWH 5RFN 5HDFWLRQ Canadian J. of (DUWK6FLHQFHV SS
>@*UDWWDQ%HOOHZ 3( Microcrystalline Quartz, 8QGXODWRU\([WLQFWLRQDQG$ONDOL6LOLFD5HDFWLRQ Proc. 9th Intern. Conf. on AAR in Concrete, London 1992, pp.
[6] Hadley, D.W.: $ONDOL UHDFWLYLW\ RI FDUERQDWH URFNV expansion and dedolomitization. Highway Research %RDUG3URFHHGLQJV SS
>@2ZVLDN = 7KH $ONDOL6LOLFD 5HDFWLRQ LQ &RQFUHWH, Polish Academy of Science, Polish Ceramics Bulletin vol. 72, Kraków 2002.
[8] Swenson, E.D., Gillott, J.E.: Characteristics of Kingston Carbonate Rock Reaction, Highway Research %RDUG3URFHHGLQJV SS
[9] Tang, M.: .LQHWLFVRI$ONDOL&DUERQDWH5HDFWLRQ, Proc. of 8th Intern. Conf. on AAR, Ed. by K. Okada, Kyoto, SS =G]LVâDZD2ZVLDN
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