الفهرس 
REVIEW ON DOLOMITE AND ALKALIAGGREGATE REACTIONSOnly 14 pages are availabe for public view
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Abstract
As a result of the huge investments in construction sector in Egypt, the demand of rocks to be used as concrete aggregate is increased. Dolomite is one of the mostly used concrete aggregate in Egypt. Ataqa area is considered as one of the biggest sources of suitable aggregate for concrete industry in Egypt. Dolomite is found in different place in Egypt such as Suez region, Nile Valley, Western Desert, Sinai, Red Sea district. This study aims to evaluate the quality of Ataqa dolomite as safe, inert, and sound source of concrete aggregate. Gebel Ataqa is located in the northern part of Eastern Desert, about 20 km south of Suez, between Latitudes of 30o 00’ and 29o 47’ N and Longitudes of 32o 16 and 32o 28’ E. with elevation 871 m. The geology of G. Ataqa has been outlined and discussed by several authors. The exposed sedimentary sequence at G. Ataqa has been subdivided into six formations ranging in ages from Cenomanian to Recent. The Eocene dolomite has lower hardness, more ability to weathering, higher porosity and pale color. It is used as building stones, filler powder. The Cretaceous dolomite has higher hardness, lower porosity and yellowish gray color. The quarries and crushers are located on eastern and northern sides of G.Ataqa, these areas are consider as a basin of accumulation of weathered rocks of G.Ataqa.
Dolomite description, genesis, textures and problems relating to the alkali- aggregate reactions (AAR), alkali-silica reactions (ASR), alkali-silicate reactions, alkali-carbonate reactions (ACR) and historical reviews of AAR in world and Egypt are reviewed.
The aim of the study is achieved by studying the different properties of rock and aggregate samples. These properties include mineralogy and petrography, physical, mechanical and chemical. The experimental work and field work have been conducted to achieve the aim of this study. Concrete trial mixes were done to check the performance of aggregate in concrete making. The field work was achieved in two levels, first level was achieved by collecting 200 single samples from quarries, the second level was achieved by collecting 9 technological samples, each one including 2 different grading sizes from 9 quarries which will be referred as Q1- Q9.
The analysis and tests were done on aggregate samples such as megascopic investigations, petrography and characteristic textures identification, mineralogical investigation using XRD analysis, chemical composition by X-ray fluorescence (XRF) and gravimetric method and physico-mechanical properties. Also, Concrete tests (fresh and hardened concrete tests) and tests of ASR and ACR were done
Petrography, X-ray diffraction (XRD), and geochemical analysis were used to identify the mineralogical and geochemical characteristics of the studied rocks at G.Ataqa and follow their vertical and horizontal heterogeneity. The petrographic description is summarized as following; Q-1and Q-2 quarry are calcareous dolomite polymodal size of very fine to coarse dolomite with euhedral to subherdal boundaries. They are characterised by selective dissolution, fissure and cavity filling. Q-3 quarry is characterized by unimodal size and polymodal sizes, low to high porosity, void and veinlet filling. Fissures are clear resulting of dissolution or cracking. Q-4 quarry is characterized by dolomite with unimodal size and polymodal sizes are euhedral, subhedral, idiotopic boundaries. Q-5 quarry is characterized by dolomite with unimodal and polymodal, cloudy dolomite, brownish color of iron, inter-particles permeability. Q-6 quarry is characterized by dolomite with polymodal size, unfilled fissures formed by dissolution, uncomplete cavity filling forming high permeability, drusy crystallization, cavities contain insoluble remains, birds eyes textures and extraclast. Q-7 quarry is characterized by dolomite with polymodal sizes, cavities filling with coarser dolomite, very low to low porosity, cloudy cores, cavity filling. Q-8 quarry is characterized by dolomite with unimodal to polymodal sizes, moldic porosity resulting from skeletal grains dissolution. Q-9 quarry is characterized by dolomite with polymodal, low to high porosity, detrital fragments of limestone, dolomite, quartz scattered in very fine matrix of dolomite. It contains well formed crystals of gypsum (selenite) and dissolved cavities.
Mineralogy of aggregates; X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material
The Lumsden formula is used to calculate the mole % of CaCO3, MgCO3 in carbonate minerals with its amounts in rocks.
Results and discussion of XRD analysis; Total dolomite ranges from 66.1 to 99.2% with an average value (91.4%). The highest value (99.2%) is recorded in Q-6 quarry and the lowest value (66.1%) is recorded in Q-1 quarry. It
increases from northern area (Q-1 and Q-2 quarries) to nearly equal percentage in central area from (Q-3 to Q-8 quarries) then decrease in Q-9. Stoichiometric dolomite ranges from 56.7 to 99.2% with an average value (80.0%). The highest value (99.2%) is observed in Q-6 quarry, meanwhile the lowest value (56.7%) is recorded in Q-1 quarry. It increases gradually at the northern parts from Q-1 (56.7%) to Q-4 (86.5%), The other quarries show variable values (62.9%, 99.2%, 85.4%, 98.1%, 89.8%). Ca-rich dolomite ranges from 0.0 to 35.3% with an average value (11.5%). The highest value (35.3%) is recorded in Q-5 quarry and the lowest value (0.0%) is observed in Q-6, Q-8 and Q-9 quarries. It increases gradually at the northern parts Q-1 (9.5%) to Q-3 (20.2%), then it oscillates in values in other quarries (9.9%, 35.3%, 0.0%,
11.6%, 0.0%, 0.0%). Total calcite ranges from 0.6 to 32.7% with an average value (7.3%). The highest value (32.7%) is recorded in Q-1 quarry and the lowest value (0.6%) is recorded in Q-6 quarry. It decreases gradually at the northern parts Q-1 (32.7%) to Q-3 (2.9%), then it shows nearly the same values with average (2.1%) for quarries from Q-3 to Q-9. Quartz ranges from 0.0 to 6.5% with an average value (1.1%). The highest value (6.5%) is observed in Q-9 quarry meanwhile the lowest value (0.0%) is recorded in Q-3 and Q-5 quarries. Q-1 to Q-8 quarries show the lowest values with average 0.4%, then Q-9 quarry shows abnormal increase 6.5%. Gypsum ranges from 0.0 to 1.6% with an average value 0.2%. The highest value (1.6%) is recorded in Q-9 quarry and the lowest value (0.0%) is recorded in Q-1 to Q-8 quarries. Gypsum shows abnormal increase (1.6%) in Q-9 quarry. The stoichiometric dolomite increases gradually from north toward south on the expense of other carbonate minerals, with abnormal lower values in Q-1 and Q-5. The Ca-rich dolomite increases gradually from north toward south reaching to maximum value (35.3%) in Q-5, then it disappears in southern area. Calcite deceases from Q-1 to Q-3, then it shows approximately the same values at Q-3 to Q-9.
The most important oxides in the studied carbonate aggregates are CaO, MgO, Fe2O3, SiO2, Al2O3 and LOI which measured by XRF.
CaO% range from 31.04 to 43.12% with an average value 35.30%. The highest value (43.12%) is recorded in Q-1 quarry and the lowest value (31.04%) is recorded in Q-9 quarry. The value of CaO is high in the northern quarries and decreases southward, which mean that limestone is more abundant in the northern quarries.
MgO% range from 9.02 to 18.90% with an average value 16.24%. The highest value (18.90%) is recorded in Q-8 quarry, meanwhile the lowest value (9.02%) is recorded in Q-1 quarry. The value of MgO is high in the central
quarries (Q-3 to Q-8) and decreases southward at Q-9 quarry and northward at Q-1 and Q-2 quarries, which mean that dolomite is more abundant in the central part of the study area.
SiO2% range from 0.37 to 3.48% with an average value 1.12%. The highest value (3.48%) is recorded in Q-9 quarry and the lowest value (0.37%) is recorded in Q-3 quarry. The distribution of SiO2 is varying in the study area and show high percentage in Q-9 quarry as a result of the presence of quartz.
Al2O3% range from 0.09 to 0.38% with an average value 0.21%. The highest value (0.38%) is recorded in Q-9 quarry and the lowest value (0.09%) is recorded in Q-6 quarry. The Al2O3 values are low which related to the presence very low amount of clay minerals in all quarries.
SO3% range from 0.14 to 1.53% with an average value 0.35%. The highest value (1.53%) is recorded in Q-9 quarry and the lowest value (0.14%) is recorded in Q-2, Q-4 and Q-7 quarries. The SO3% is very high in Q-9 quarry resulting from the presence of gypsum in this quarry.
It is evident that all studied quarries could be considered as sources for concrete aggregates. The mineral composition of all quarries aggregates includes dolomite, calcite, quartz and gypsum whereas the major mineral is dolomite. Both, the natural and fine contents of the aggregates are generally in direct proportion.
The maximum unit weight (1477kg/m3) with the minimum water absorption (0.60%) of the quarry aggregates is recorded in Q7 sample, however, Q9 aggregates are showing lower unit weight (1344kg/m3) and maximum water absorption (2.10%).
The mineral content affect on the crushability and the abrasion of the aggregates. The Q8 of 98.10% dolomite shows the maximum crushing value (25.4%), however, the Los Angeles is maximized in Q9 aggregates (29%) due mainly to its highest water absorption and medium to high porosity. On the other side, the flakiness and elongation indices could not be related to the mineral contents or the microstructure of the aggregates.
Two mix designs have been prepared to test the technical properties of the concrete containing the nine quarry aggregates. The first mix was designed using 350Kg cement and 0.55 w/c ratio whereas the second mix was designed on the base of 450Kg cement and 0.40 w/c ratio.
Different fresh concrete properties were measured such as ambient concrete temperature, slump (at 10, 30 and 60 minutes), initial setting time, unit weight, yield and air content. After pouring in 150mm cubes and the aging for 3, 7, 28
and 365 days, the compressive strength of the cubes was calculated. Water penetration depth of the concrete cubes was determined also after 28 days. The length change of concrete bars 3” x 3” x 11” was also measured after 3, 6, 12
months and 2 and 7 years.
The average unit weight of fresh concrete is maximum in Q7-350 (2398kg/m3) and Q7-450 (2439kg/m3) mixes due mainly to the highest unit weight of the Q7 aggregates (1353 kg/m3) with the accompanied lowest water absorption (0.6%). The compressive strength of all the 350- and 450-kg/m3 mixes increase proportionally in the direction 3, 7, 28 and 365 curing days. The 350 and the 450-kg/m3 concrete cubes exceed the 300kg/cm2 and 450kg/cm2, respectively, which are the average standard limits adopted by the Egyptian code.
The average compressive strength values of all mixes are completely matching with the measured average water penetration depth. It is proved that Q7-350 and Q7-450 kg/m3 mixes are of the minimum recorded water penetration depths (20 and 15mm, respectively).
The total alkali content of any concrete mix should not exceed 3kg/m3. The 350kg/m3 concrete mixes of this study are in the acceptable alkali content, however, those of the 450kg/m3 concrete mixes are all out of limit due mainly to the higher proportions of cement.
There is no physical evidence for the alkali silica reaction of the studied concrete mixes. This could be attributed to the absence of any active silica in any of the quarry aggregates. The measured mortar bar length changes are below 0.1% which is the acceptable limit for alkali silica reaction in all samples.
All the concrete mixes were tested against the possible alkali carbonate reactions. The acceptable limit of expansion after 1 year of curing is 0.03%. this limit is achieved for most 350Kg/m2 mixes except for Q4 for 7 years, Q1 mixes at 2 and 7 years and Q9 mixes at 1, 2 and 7 years and the 450 kg/m3 mixes are mostly exceeding the expansion acceptable limit at 7 years except Q2, Q6.
There is a physical evidence to show this alkali carbonate reaction (expansion). The microstructure of the 3 months curing Q9-450kg/m3 concrete cube is showing rim of calcite around dolomite aggregate, it may be as result of alkali carbonate reaction activated by calcium liberated from dissolved gypsum or dedolomitization take place by weathering of aggregate before concrete making.
According to the current thesis tests and analysis, the studied dolomitic aggregates can be classified according to its mineralogy, chemical impurities, strength, water absorption, pores, alkali-silica reaction, alkali-carbonate reaction to five grades;
1- Grade-1: Quarries are mainly stoichiometric dolomite, most stable, and less expansion as Q-6 quarry.
2- Grade-2: Quarries contain combination of stoichiometric and Ca-rich dolomite, with lower stability than grade # 1 such as Q-3, Q-4, Q-5, Q-7, Q-8 quarries.
3- Grade-3: Quarries contain calcite dolomite with low calcite percentage (≤30 %) give low potential of ACR such as Q-2 quarry.
4- Grade-4: Quarries contain calcite dolomite with high calcite percentage (>30 %) give high potential of ACR such as Q-1 quarry
5- Grade-5: Quarries contain stoichiometric dolomite, high natural aggregate% (weathered aggregate) and high percentage of gypsum that causing expansion as result of internal sulphate attack and liberate calcium that increase the risk of dedolomitization such as Q-9 quarry.
Recommendations
The best choice is dolomite with Grade-1, the user can use it without precautions.
Dolomite with Grade-2 can be used with no or little precautions.
Carbonate of Grade-3 can be used with precautions, in dry environment as superstructure, and should be far from marine constructions, hydraulic constructions. and substructures.
Carbonate of Grade-4 is high potential reactive, so, its using is prohibited
Don’t use carbonate of Grade-5 at all.