Most of the crushed-rock aggregate produced in Türkiye comes from limestone quarries; along the Aegean and Mediterranean coastal belt the proportion is even higher. Even so, two extreme views about limestone circulate in the field: to some tradesmen limestone suits every job, while to some engineers it is a soft, unreliable stone. Both are incomplete. If you know how limestone forms, how its chemistry speaks to cement, and which of its limits comes into play in which use, you will read both material selection and test reports correctly. This guide builds that framework through the eyes of a producer operating a limestone quarry in Milas.
How limestone forms: the short story of a sedimentary rock
Limestone is a sedimentary rock whose main constituent is calcium carbonate (CaCO3). Mineralogically this carbonate occurs mostly as calcite, accompanied in smaller proportions by aragonite and magnesium-bearing dolomite. Most of the rock accumulated in shallow, warm marine environments. When corals, shelled organisms, algae and microscopic plankton die, their shells sink to the sea floor; the pressure of the overlying sediment and the carbonate-rich waters percolating through over time turn this mass of shells into stone. Some limestones form directly by chemical precipitation, when water reaches carbonate saturation and deposits calcite; travertine and oolitic limestone belong to this group.
This mode of formation determines several basic characteristics of limestone. First, the rock is bedded; in the quarry it appears layer upon layer, and each layer may differ from the previous one in density, colour and clay content. Second, pure limestone is rare; most limestone carries clay, silt, organic matter or siliceous nodules (chert, flint). Third, because carbonate dissolves in water and acid, limestone masses karstify over time: caves, solution cavities and fissures filled with red soil form. These three features explain why stone from different faces of the same quarry can give different test results.
Two rocks are often confused with limestone. Dolomite consists of calcium-magnesium carbonate; it looks very much like limestone but reacts more weakly with dilute acid and is usually somewhat harder and denser. Marble is limestone that has recrystallised under high temperature and pressure, that is, undergone metamorphism. Muğla's famous marbles are the product of exactly this transformation; their chemistry is the same as limestone, their texture is different.
The prevalence of limestone around Muğla and Milas
South-west Anatolia is a region geologically dominated by carbonate rocks. Large areas in and around Muğla are covered by the remains of thick carbonate platforms that accumulated in shallow seas during the Mesozoic. To the north of the region lie the metamorphic rocks and marbles of the Menderes Massif; to the south and west lie the stacked thrust sheets of bedded limestone and dolomite known as the Lycian nappes. Milas and its immediate surroundings sit at the intersection of these two great units, which is why both recrystallised, hard limestones and younger, less compacted carbonate beds are found here.
In the field this means one thing: finding limestone reserves in the region is not hard; finding the right limestone is. One flank of a hill may yield a dense, grey-blue, sound limestone that breaks with sharp edges, while the other flank shows a yellowish, more porous level with clayey interbeds. In karst areas, the red clay that accumulates as fissure fill degrades the fines quality of the product if it gets into the crushing-screening plant. That is why quarry selection, which level to dig on the face and how to manage the overburden are the first and most decisive step in product quality.
Another advantage of the region's limestone is logistics. Ready-mixed concrete, road and infrastructure work is intense along the Aegean and Mediterranean coast, and because aggregate is a bulky, heavy material, transport costs weigh heavily even over short distances. Having the source close to the point of use lowers both cost and carbon footprint. How tonnes and cubic metres are calculated for haulage is explained in detail in the article on aggregate m3-tonne conversion and haulage.
The strengths of limestone as an aggregate
The most valued property of limestone as an aggregate is its relationship with cement paste. Cement clinker is itself largely made from limestone; the calcium silicate hydrate gel and calcium hydroxide formed during hydration share a chemically kindred environment with the calcite surface. This affinity helps the transition zone where aggregate and cement paste meet (the interface) to be denser and less porous. In siliceous aggregates the interface is usually the weaker link; in limestone this link knits together better. The result is better bond at the same cement content and, more often than not, slightly higher tensile and flexural strength.
The second strength is its fracture behaviour. Limestone breaks more easily in the crusher than basalt or quartzite, and on a properly set-up crushing-screening line it yields cubical, well-shaped particles. Because the proportion of flaky and elongated particles can be kept low, concrete workability improves, pumping becomes easier, and less water and admixture are needed for the same slump. In road layers, cubical particles interlock and compact better.
Third, the fines generated during crushing. Limestone dust, that is, stone dust, is not harmful in concrete as long as it contains no clay; on the contrary, it is beneficial: it fills voids, gives the mix a richer, more cohesive body and reduces segregation. This is why limestone filler is regarded as a self-made admixture. The fact that limestone's coefficient of thermal expansion is close to that of cement paste also limits internal stresses under temperature changes; in mass concrete and in slabs exposed to the sun, this is an advantage not to be underestimated.
Finally, limestone is basic in its surface chemistry. It bonds well to acidic binders such as bitumen and to cement; this property becomes even more important in asphalt and is discussed separately below.
The limits of limestone: abrasion, acid and variability
Limestone's most debated weakness is its resistance to abrasion and impact. Calcite is a medium-to-soft mineral on the Mohs hardness scale, softer than silicate minerals such as quartz, feldspar and pyroxene. As a result, the Los Angeles abrasion loss of limestone aggregate is generally higher than that of basalt or granite. But this generalisation does not apply with equal weight to every limestone. Recrystallised, dense-textured, low-porosity limestones perform far better than loose, shelly ones. This is where quarry selection and level control come in; the abrasion values of two different benches in the same quarry can diverge considerably.
The second limit is acidic environments. Calcium carbonate reacts with acid and dissolves. In industrial wastewater structures, some agricultural facilities, chemical storage areas or ground with acidic groundwater, the surface of concrete made with limestone aggregate can wear away over time. In such environments either siliceous aggregate is preferred or the aggregate is protected by the impermeability and coating of the concrete. In ordinary building concrete, road and infrastructure work this risk does not arise; limestone's sensitivity to acid is a question to be asked at the design stage for special environments.
The third limit is porosity and water absorption. Some limestones have low water absorption, while shelly, chalky types and those with solution cavities absorb more water. High water absorption reduces freeze-thaw resistance, complicates the water-cement ratio calculation in concrete and increases bitumen consumption in asphalt. The fourth limit is clay contamination; clay from karst fissures degrades the fines quality and raises the methylene blue value. This subject is covered in detail in the article on how aggregate quality affects concrete.
The common thread running through these limits is this: in limestone aggregate, quality is read not from the name of the rock but from the measured properties of that particular level in that particular quarry. Without water absorption, Los Angeles, sand equivalent and petrographic examination results, it is not right to declare a limestone good or bad.
Limestone aggregate in concrete: coarse, fine and filler
The basic standard for concrete aggregate in Europe and Türkiye is TS EN 12620, and it classifies aggregate not by rock type but by measured properties. In other words, a limestone aggregate can be used in any concrete class once it meets the requirements for grading, shape, abrasion, water absorption, clay content and chemical purity. A significant share of ready-mixed concrete production in Türkiye is already made with limestone coarse aggregate and limestone crushed sand.
As coarse aggregate, limestone performs without problems in most structural concrete (foundations, columns, beams, slabs, shear walls). In high-strength concrete, however, the strength of the aggregate itself starts to become decisive; in this class the dense, low-porosity types of limestone are required and verification is done with trial mixes. As fine aggregate, limestone crushed sand demands a little more water than natural sand because of its angular particle shape, but it interlocks better with the cement paste and has a positive effect on strength. Limestone dust at filler size is used in self-compacting and pumped concretes as a component that regulates viscosity.
The points needing special attention in mix design with limestone are these: the water absorption value must be added to the mix water, the filler content must be considered together with the superplasticiser dosage, and whether the fines are stone dust or clay must be verified with sand equivalent and methylene blue tests. For which fraction is used in which concrete class, see the guide to choosing size fractions.
Limestone in road base and asphalt
In a road structure, limestone can appear in every layer from the fill and sub-base at the bottom up to the wearing course; but each layer expects something different from it. What the sub-base and base layers need is a granular skeleton that spreads the load when compacted, provides drainage and stays stable against seasonal movement. Sub-base aggregate and plant-mix base produced from crushed limestone play this role well: cubical particles interlock well under compaction, the fines help the layer close up, and the strength of the particles is sufficient for spreading the load. What sub-base aggregate is and what it does within the layer is explained in detail in the article on what sub-base aggregate is.
Moving up into the asphalt layers, expectations tighten. In bituminous base and binder courses limestone aggregate is common and successful; its basic surface forms a strong bond with bitumen, and the risk of stripping is lower than with siliceous aggregates. This is perhaps limestone's least known but most valuable advantage in asphalt work. In the wearing course the picture is mixed. In this layer, on which traffic rolls directly, the aggregate must resist polishing, that is, it must keep its texture under tyre friction. Here the softness of calcite works against it: many types of limestone polish over time, and skid resistance on a wet surface drops. For this reason, on heavily trafficked roads either a hard rock is chosen for the wearing course or limestone is used blended with a hard aggregate. All the tests and properties expected of asphalt aggregate are covered in the asphalt aggregate article.
In summary, limestone's place in the road structure depends on the layer: in the base and binder courses it is almost the natural choice, while in the wearing course it is a decision that depends on the traffic class and the measured polished stone value.
Where limestone stands on alkali-silica reaction
Alkali-silica reaction (ASR) occurs when the alkalis in cement react with reactive silica minerals in the aggregate to form a water-absorbing gel; the gel swells, the concrete cracks from within, and the damage surfaces years later. The raw material of the reaction is reactive silica: poorly ordered forms such as opal, chalcedony, cryptocrystalline quartz and volcanic glass. Since pure limestone contains none of these minerals, limestone aggregate is generally considered low-risk with regard to ASR. This is one of the reasons limestone is used so widely in Türkiye.
Two details must not be overlooked, however. First, some limestones carry nodules of chert or flint, and these nodules consist of precisely the cryptocrystalline silica that causes ASR. An aggregate that looks like limestone can turn out to be reactive if its chert content is high. This is why petrographic examination of the quarry levels is not merely an academic formality but a genuine risk filter in the field. Second, some types of dolomitic limestone can exhibit a different mechanism known as alkali-carbonate reaction; it is rarer, but it matters because, once identified, there is no practical remedy other than changing the aggregate.
What needs to be done in practice is simple: when a new source is brought on stream, a petrographic analysis is commissioned, and if there is any doubt, expansion is measured with an accelerated mortar bar or concrete prism test. If working with an aggregate found to be reactive is unavoidable, the reaction can be suppressed with low-alkali cement or pozzolanic additions such as fly ash or ground granulated blast-furnace slag. Limestone's advantage in this picture is that in most cases it makes these precautions unnecessary.
Choosing the right limestone: what to ask in the field
The questions you should ask when buying limestone aggregate concern not the name of the rock but its measured properties. For coarse aggregate: Los Angeles abrasion loss, water absorption, flakiness index and magnesium sulfate soundness (freeze-thaw) loss; for fine aggregate: sand equivalent, methylene blue value and grading; and for both, the petrographic examination result. That these values are current and represent the level the product actually comes from matters as much as the test report itself.
The second question is production consistency. In a good limestone quarry the faces are worked to plan, clayey levels are kept separate, the crushing-screening line controls the fines by washing or dry screening, and regular internal control tests are carried out. If the product is good one week and clouded with clay the next, the test report means nothing.
İTS Maden produces aggregate fractions, crushed stone, sub-base aggregate, plant-mix base and run-of-quarry material at its limestone quarry in Milas with this understanding. You can review our product fractions and our approach to quality control, and contact us for the right material for your project.
