Properties of Coarse Mineral Aggregates Against Properties of Concrete

K e y w o r d s : Compressive and tensile strength of concretes; Properties of aggregates; Strain properties of concretes; Stress – strain relationships. 3/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 97 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 3/2018 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 8 0 4 2 W . P i a s t a , W . B u d z y ń s k i , J . G ó r a strength from 120 MPa to 260 MPa [2]. Basalts show the variability of characteristics within their mineral composition, but also within one bed. The best properties are those of rocks from volcanic vents, and the worse ones derive from coastal areas of lava covers, which are more susceptible to weathering. The occurrence of basaltic sunburn crackings is risky for concrete [3]. Big advantages of basalt rocks are high strength and a very fine-grained texture, due to which the grain of the crushed aggregate is characterized by micro-roughness which ensures good adhesion of the hardened cement paste to the grains [4], [5]. Granite as a plutonic acid igneous rock containing quartz in the amount of up to even 60.0% by volume, alkali feldspars, plagioclases and biotite, is a valuable building material. However, it is found to be of quite variable properties dependent on the bed, and sometimes on the degree of weathering. Strength of Polish granites is from 100 MPa to 210 MPa, porosity from 1.5% to 3.0%, absorption from 0.2% to 0.5% [2]. for the production of aggregates, granite is taken primarily from beds in the Strzegom-Sobotka Massif, but unfortunately the properties of this rock are pretty average, as compared to other Polish granites, for example, from the Strzelin Massif. And as demonstrated one can also have reservations towards the properties of concretes made from these aggregates [6], [7], [8]. Carbonate rocks from the limestone – dolomite group, which are a mixture of calcite and dolomite, are of great importance in aggregates used for concrete. While selecting rocks for the production of aggregate to be used for concrete the most important role is that of the porosity it is highly desired to be as low as possible, and much less important is the amount of calcite and dolomite in the rock. Devonian limestone and dolomites are of the lowest porosity. In the best limestone, the absorption is less than 1.0%, and the strength higher than 100 MPa. Strength of the Devonian dolomite or calciferous Devonian dolomites is even higher, often exceeding 130 MPa, and sometimes even 200 MPa [9]. Aggregates from carbonate rocks, despite their low hardness and usually lower strength than that of the igneous rocks and quartzite sandstones, have gained considerable technical appreciation as a dense interfacial transition zone is formed at carbonate aggregate grains [7, 10, 11, 12]. Among sedimentary rocks, there are also sandstones, which are used for the production of concrete aggregates. Quartzite sandstones have high physical properties and they are readily used for aggregate production. They consist of compressed quartz grains with crystallized quartz cement, the same as specific quartzites – which are metamorphic rocks of Precambrian origin [2]. Compressive strength of Cambrian quartzite sandstones exceeds 200 MPa, and the Devonian 150 MPa, absorption is less than 0.6%. The SiO2 content is more than 95.0%, and sometimes even 99.0% [13]. Thus, they are ultraacidic rocks. Petrographic composition of natural aggregates can be very complex. In gravels, (especially those from Northern Polish Lowland and Lower Silesia Region), there may be grains of both strong igneous rocks and of weak sedimentary rocks. The quality of concrete with gravel is fundamentally influenced by its petrographic and mineral composition. Significant importance for the physical properties of concrete has a content of weak grains, which are derived from weak and weathered rocks, such as for example porous sandstones or fossilized limestone. One should avoid gravels as well as any rock aggregates which contain minerals susceptible to adverse reactions with components of the cement paste. Aggregates containing reactive silica in forms such as opal, chalcedony, tridymite or strained quartz belong to the most susceptible to alkali-silica reaction that causes expansion of concrete [14]. These minerals occur in chert, andesite, rhyolite tuff, dacite, porphyry, fossilized limestone and strained quartz in granitic rocks, as well as in many gravels [15, 16]. Crushed aggregates are obtained directly from rock material breaking, thus the properties of those aggregates are associated to a great extent with the mineral composition and the properties of individual rock. However, in the case of natural gravel aggregates, consisting of grains of different petrographic origin, and hence of the properties often very diverse and varying depending on the location of the bed, such a direct correlation does not exist. Evaluation of the quality of aggregates was accurately recognized in the standard [17]. Specific requirements were determined in the range of aggregate crushing strength. It is measured with aggregate crushing value (ACV) for any fraction individually [17]. The crushing strength is reduced by irregular grains and therefore their content should be tested. Other necessary tests to be carried out concern the content of dust in aggregate. Covering the aggregate grain the dust decreases aggregate-cement paste bond strength and weakens the strength of concrete. Adhesion of the paste to aggregate is significantly affected by the texture of the grains [18, 19]. As 98 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 3/2018 P R O P E R T I E S O F C O A R S E M I N E R A L A G G R E G A T E S A G A I N S T P R O P E R T I E S O F C O N C R E T E emphasized with respect to aggregates made from basalt rocks. 2. MATERIALS AND TEST METHODS The tests involved five coarse aggregates of two fractions 2-8 and 8-16 mm. There were 4 crushed aggregates: granite, basalt, dolomite, quartzite sandstone and natural gravel. Aggregates came from the following Polish rock beds: granite – Graniczna quarry, Strzegom Massif – Sobótka; basalt – Gracze quarry, valley of Nysa Kłodzka; dolomite – Laskowa Góra quarry, Świętokrzyskie Mountains; quartzite sandstone – Wiśniówka quarry, Świętokrzyskie Mountains natural gravel – gravel plant Suwałki. Basic properties of the rocks were shown in Table 1. In order to identify the mineral composition, the X-ray diffraction of aggregates was carried out. Aggregates were tested in terms of grain composition, crushing strength, absorption by weight, content of irregular grains and mineral dust, as well as bulk and specific density, on the basis of which the total porosity was determined. In order to determine the effect of the coarse aggregate type on the properties of concrete, the 5 concretes made with those aggregates were tested. The same volume of coarse aggregate in each concrete was considered. The value of the w/c was 0.58. Portland cement CEM I 42.5 R was applied. The composition of concrete mixtures was given in Table 2. 3. DISCUSSION 3.1. Tests results of aggregates In basalt (Fig. 1) two basic minerals were found: plagioclase – in the form of anorthite (calcium aluminosilicate) and pyroxene – in the form of augite (magnesium and iron silicate), and a very small amount of olivine. There is no quartz in basalt. In granite (Fig. 2) the dominant mineral is quartz, and next to it two feldspars orthoclase (potassium aluminosilicate) and albite (sodium aluminosilicate). Furthermore, there is biotite in the rock (basic potassium aluminosilicate, magnesium and manganese) which is the main component of mica. On the basis of diffraction patterns (Figs 3 and 4), it was found that the composition of dolomite and quartzite sandstone is of mono-mineral character. The aggregate from Laskowa Góra contains practically dolomite only (CaMg(CO3)2). There are only trace elements of calcite and quartz. However, the aggregate made form quartzite sandstone contains quartz only (SiO2). Other minerals, by using X-ray diffraction were not found. The most complex is the petrographic and mineral C I V I L E N G I N E E R I N G e 3/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 99 Table 2. Composition of concrete mixtures concrete components concretes designation (type of coarse aggregate) B 058 (basalt) G 058 (granite) D 058 (dolomite) K 058 (quartzite) Ż 058 (gravel)