Evaluation of engineering properties of scoria in central Harrat Rahat, Saudi Arabia. Introduction

Size: px

Start display at page:

Download "Evaluation of engineering properties of scoria in central Harrat Rahat, Saudi Arabia. Introduction"

Leon Barrett
6 years ago
Views:

1 Evaluation of engineering properties of scoria in central Harrat Rahat, Saudi Arabia A. A. Sabtan 7 W. M. Shehata Abstract Although black scoria deposits occur extensively in western Saudi Arabia, there has been little work undertaken on its engineering characteristics as a light-weight aggregate which can be used in concrete for structural, masonry and insulating purposes. In an attempt to remedy this, central Harrat Rahat was selected for an engineering evaluation of scoria deposits in the vicinity of major cities where it may provide an easily accessible resource for natural aggregate. The petrography of the scoria and the deleterious material content were found to be acceptable by ASTM standards, but grading analyses indicated it would need to be processed before use. The other physical properties of the scoria such as bulk density, specific gravity and absorption indicated that samples from Jabal Halat Ash Shaykh quarry gave acceptable results. The porosity of the scoria is relatively high and some of the pore spaces are not interconnected. The material is pozzolanically active and can be also used as an additive to Portland cement. Résumé Bien que les dépôts de scories volcaniques noires soient largement répandus dans l ouest de l Arabie Saoudite, il y a eu peu de travaux portant sur leurs caractéristiques techniques, comme granulat léger susceptible d être utilisé comme constituant de bétons de structure, de construction ou matériaux d isolation. Dans le but d y remédier, la région du central Harrat Rahat fut sélectionnée pour une caractérisation technique des dépôts de scories au voisinage de grandes villes susceptibles d être approvisionnées facilement par de tels granulats. La nature pétrographique des scories et leur teneur en éléments indésirables satisfont aux normes ASTM mais les analyses granulométriques ont montré qu il faudra procéder à certains traitements avant usage. Les propriétés physiques des scories telles que la masse volumique, la densité de la matrice et les propriétés d absorption obtenues à partir d échantillons de la carrière de Jabal Halat Ash Shaykh, sont apparues correctes. La porosité des scories est relativement forte et certains espaces poreux sont non connectés. Les scories présentent des propriétés pouzzolaniques et peuvent aussi être utilisées comme ajout au ciment Portland. Keywords Scoria 7 Physical properties 7 Saudi Arabia 7 Light-weight aggregate 7 Harrat Rahat Mots clés Scories 7 Propriétés physiques 7 Granulats légers 7 Harrat Rahat 7 Arabie Saoudite Introduction Received: 16 April Accepted: 25 March 2000 A. A. Sabtan 7 W. M. Shehata King Abdulaziz University, P.O. Box 1744, Jeddah 21441, Saudi Arabia esa30016kaau.edu.sa Strombolian-type explosions have formed numerous scoria pyroclastic cones within the basaltic lava fields in western Saudi Arabia. These basaltic lava fields are locally known as harrats and they extend in a north-south direction covering about 180,000 km 2. As shown in Fig. 1, Harrat Rahat is in a central position and is accessible by the Jeddah-Madinah highway. Scoria in Harrat Rahat exists Bull Eng Geol Env (2000) 59 : Q Springer-Verlag 219

2 A. A. Sabtan 7 W. M. Shehata Aggregate properties Sampling Several trenches were excavated in the four sites in addition to the main pit and the existing test pits at Jabal Halat Ash Shaykh. Samples representing the exposed thickness of the black scoria layer in a total of 17 trench or test pits were taken from the four sites, in addition to three samples from the 16-m-thick black scoria layer in the main pit. The trenches which exposed and red, altered or dirty scoria were ignored. The samples were broken down in the field to laboratory-size samples according to ASTM C-702. Fig. 1 Location map of Harrat Rahat with respect to the other harrats either in the form of cones or as deposits in the vicinity of the cones formed by wind action during an eruption or by subsequent erosion. Scoria has a number of industrial uses which make it potentially attractive for exploration and economic exploitation. It can be utilised as light-weight aggregate, as a source of pozzolan for the manufacture of Portlandpozzolan cement and as an insulating material, as well as having many other industrial uses (Abdul Hafiz et al. 1998; Moufti et al. 1998, 1999). The selection of the central section of Harrat Rahat for this study was based on its accessibility, its vicinity to the major cities in northwestern Saudi Arabia and the presence of a scoria quarry operated by the CIC company which exposes the scoria at depth. The scoria reserves in Saudi Arabia are extensive. No serious assessments were made as to the quantity or the quality of these deposits. The estimated reserves in the four locations investigated within central Harrat Rahat namely Jabal Halat Ash Shaykh, Jabal Al Hala, Jabal Suwah and Jabal As Sahiliyah amount to 5 million m 3 (Moufti et al. 1998). The objective of this paper is to describe the engineering properties of the scoria present in these locations as the start of a technical engineering program to evaluate the rest of the resources. Petrography Petrographic examination of the scoria was performed to satisfy ASTM C-295. The scoria, in its natural condition, occurs as layers formed mainly of loose particles with a maximum grain size of 20 mm. The particles are mainly subrounded, angular to subangular and with rough to very rough surfaces. The scoria is black to blackish-grey in colour when fresh and changes to deep brown or yellowish-brown on weathered surfaces. It is generally of a basaltic composition with vesicles, a glassy matrix and some phenocrysts. The vesicles constitute more than 60% of the material mass. They are of different shapes (spherical, subspherical, ovoid, lobate and sometimes irregular) but with limited size variations (up to 5 mm). Some of the vesicles are interconnected, while others are not connected. In some altered scoria, the vesicles are totally or partially filled with secondary minerals (carbonates, quartz and possibly zeolites) and brownish amorphous material. The ground mass containing the vesicles consists of dark blackish volcanic glass with dusty iron oxides. The phenocrysts consist of clinopyroxene, plagioclase and rare olivine. The clinopyroxene occurs as colourless microphenocrysts of euhedral to subhedral diopside while a few of the crystals are pale-green aegerine. The plagioclase occurs as randomly oriented microlites and the relatively coarse crystals have the composition of calcic labradorite. Other accessory minerals such as apatite, magnetite and spinel are also present in small amounts. Deleterious substances The following five types of deleterious substance may be found in the coarse scoria and the last three in the fine scoria. 1. Particles sensitive to chemical reactions One of the main purposes of examining the petrography of the aggregate is to identify any existing particles sensitive to chemical reactions. A number of minerals or forms of silica are known to be reactive with alkalies. These are intermediate to acid (silica-rich) volcanic glass and certain zeolites. Since the volcanic glass constituting the scoria is basic (silica-deficient), it can be assumed to be non-reactive with the alkalis. The alkali reactivity of mortar cubes made of scoria was tested for the alkali reactivity (Moufti et al. 1999) and they were found to be non-reactive. 220 Bull Eng Geol Env (2000) 59 : Q Springer-Verlag

3 Engineering properties of scoria Furthermore, this proves that the zeolites which may occur in the scoria are also not deleterious. 2. Particles with physical defects concerning abrasion resistance and soundness The Los Angeles abrasion test as recommended by ASTM C-131 requires a certain grading which did not exist in any of the available scoria samples. Alternatively, the impact value test suggested by the British Standards Institution (1975) was performed on the material passing the 14-mm BS test sieve and retained on the 10-mm sieve. Eight samples were tested, giving impact values ranging between 23.6 and 54.0%, with an average of 40.2% and standard deviation of 11.4%. The Los Angeles abrasion values were estimated using the correlation suggested by Kazi and Al- Molki (1982) and were found to range between 32.5 and 74.4%, with an average of 55.4% and standard deviation of 15.7%. The Los Angeles abrasion value would not be unacceptable for normal aggregate, but there are no required specifications for light-weight aggregate. The tests were performed only for the sake of comparison. The soundness test was performed on the coarse scoria according to ASTM C-33 using the magnesium sulphate method. The average maximum weight loss after five cycles was 4.3%, which is very low compared to the maximum allowable loss of 18% for coarse aggregate and 15% for fine aggregate (ASTM C-33). The pozzolanic activity of the scoria, as will be discussed later, could have contributed to its low soundness values. 3. Clay lumps and friable particles The clay lumps were determined according to ASTM C-142 in the size fractions of passing sieve #4 (~4.75 mm), 3/ 8 in. to #4 and 3/4 to 3/8 in. Figure 2 shows the variations in the clay lump content in the different size fractions. The clay lumps in the fine aggregate (~4.75 mm) ranged between 0 and 2.9%, with an average of 1.1% and standard deviation of 0.7%, which satisfies the upper limit of 3% required by ASTM C-33 for fine aggregate. The clay lumps in the coarse aggregate (3/4 in.-#4) ranged between 0.1 and 2.6%, with an average of 1.3% and standard deviation of 0.7%. These values also satisfy ASTM C-33. However, they do not satisfy the upper limit required for light-weight aggregate of 2% for structural concrete (ASTM C-330) and concrete for masonry units (ASTM C-331). The proportion of clay lumps in the scoria samples obtained from Jabal Halat Ash Shaykh quarry main pit, which is more than 18 m deep, ranged between 0.7 and 1.2%, with an average of 1.0%, which satisfies the ASTM requirements. It is clear therefore that the clay lumps exceed the specification only in the shallow trenches which were dug to a maximum depth of 3.5 m. 4. Material finer than 75 mm (sieve #200) The material finer than 75 mm which represents the dust in the scoria was tested according to ASTM C-117. The dust was found to increase near the ground surface and decrease with depth. In the scoria samples taken from the dug trenches, the percentage of the material finer than Fig. 2 Clay lump content in the different scoria size fractions 75 mm ranged between 0.8 and 3.4%, with an average of 2.0% and standard deviation of 0.8%. ASTM C-33 allows only 1% of material finer than 75 mm in the coarse aggregate, but the percentage can increase to 1.5% if the fines are free of clay or shale. The material taken from Jabal Halat Ash Shaykh quarry main pit shows material finer than 75 mm ranging between 0.4 and 0.6%, with an average of 0.5%. The results indicate that the bulk deposit of the scoria at depth satisfies the ASTM C-33 requirements for both the range and average proportion of material finer than 75 mm. 5. Organic matter Organic material may include coal and lignite, which tend to occur as mechanically weak particles. The scoria, being of volcanic origin, would not be expected to have any coal or lignite, hence the simple qualitative colour test given in ASTM C-40 may be enough to identify the organic matter in the aggregate. The loss on ignition test suggested by ASTM C-114 reports the loss on ignition due to moisture and CO 2 produced by the combustion of the organic material and was undertaken on several scoria samples. The percentage of the material lost on ignition ranged between 1.37 and 1.42%, with an average of 1.41%. As the average moisture content in the tested samples was 0.66%, the Bull Eng Geol Env (2000) 59 : Q Springer-Verlag 221

4 A. A. Sabtan 7 W. M. Shehata average percentage of the organic matter can be estimated as 0.75%. ASTM C-33 sets an upper limit for the organic impurities (coal and lignite) of 0.5% where surface appearance is important and 1.0% for all other concrete. As the scoria is already black in colour, the surface appearance becomes immaterial and the 0.75% of organic matter satisfies the ASTM C-33 requirements. As a light-weight aggregate, ASTM C-330, C-331 and C-332 give higher upper limits of loss on ignition (5%) and the scoria therefore satisfies the requirements for structural concrete, concrete masonry units and insulating concrete. Grain size distribution The scoria, in its natural form, is well graded and could be classified as GW according to the Unified Soil Classification System (Terzaghi and Peck 1968). The gradation curves of the material (Fig. 3) partly fit within the limits given by the ASTM for light-weight aggregate for structural concrete (ASTM C-330), concrete masonry units (ASTM C- 331) and for insulating concrete (ASTM C-332). There is no doubt that the grading of the aggregate as such affects the workability of a concrete mix. Workability in turn affects the water and cement requirements, controls segregation and also affects strength, shrinkage and durability of hardened concrete. In its natural condition, the scoria does not have the right particle size to produce concrete of acceptable quality, hence it must be processed before use in a mix. The fineness modulus ranges from 4.8 to 5.8 with an average of 5.4 for the material from Jabal Halat Ash Shaykh, 4.8 to 5.6 with an average of 5.3 for the material from Jabal Al Hala, 5.4 to 5.9 with an average of 5.7 for the material from Jabal Suwah and 5.6 to 6.0 with an average of 5.8 for the material from Jabal As Sahiliyah. Although the fineness modulus alone cannot be used as a description of the grading of an aggregate, it is valuable for measuring slight variations in aggregate from the same source. The average fineness modulus values from the four locations ranged from 5.3 to 5.8, showing variations of 9% which exceeds the upper limits suggested by ASTM C-331 but satisfies the limit suggested by ASTM C-332. The uniformity of grading is of no concern if the scoria is used in manufacturing insulating concrete but should be observed if the material is to be used in manufacturing concrete masonry units. Bulk density The bulk density (unit weight) of the scoria samples was tested according to ASTM C-567. The bulk density values were reported both as rodded density and loose density. The rodded density values ranged between 740 and 1020 kg/m 3, with an average of 866 kg/m 3 and standard deviation of 83 kg/m 3, while the loose density values ranged between 660 and 870 kg/m 3, with an average of 776 kg/m 3 and standard deviation of 66 k g/m 3. ASTM C- 330, C-331 and C-332 require a maximum dry loose unit weight of 880 kg/m 3 for coarse aggregate and 1040 kg/m 3 for combined fine and coarse aggregate. The tested scoria satisfies all the ASTM specifications. Figure 4 indicates a reasonable relationship between the rodded density and loose density, such that one can be estimated from a knowledge of the other. Specific gravity (relative density) The bulk specific gravity (dry), bulk specific gravity (saturated surface dry) and apparent specific gravity of the natural scoria retained on sieve #4 (4.75 mm; coarse aggregate) and the material passing it (fine aggregate) were determined according to ASTM C-127 and C-128 respectively. Figure 5 shows the range and average specific gravity values of the coarse and fine scoria. The maximum numerical differences between values calculated on ovendried and natural samples are 0.72 for the coarse aggregate and 0.75 for the fine aggregate. These differences are relatively high and should be taken into consideration in the mix design. Water absorption The water absorption of both coarse and fine scoria was tested according to ASTM C-127 and C-128 respectively. Fig. 3 Grain size distribution curves of scoria samples (dashed lines). Solid lines show ASTM-required upper and lower limits for coarse aggregate Fig. 4 Relationship between loose density and rodded density 222 Bull Eng Geol Env (2000) 59 : Q Springer-Verlag

5 Engineering properties of scoria Fig. 6 Relationship between water absorption and specific gravity for a coarse scoria and b fine scoria Fig. 5 Specific gravity values for coarse and fine scoria The absorption of coarse aggregate ranged between 9.0 and 20%, with an average of 13.1% and standard deviation of 3.3%, and that of fine aggregate between 4.3 and 11.1%, with an average of 7.5% and standard deviation of 2.2%. Water absorption should not exceed 3% for normal aggregate (Collis and Fox 1985) but can be up to 30% for lightweight aggregate (FIB 1983). Water absorption has a considerable effect on the workability of the mix and the uniaxial compressive strength of the concrete, hence it is an important consideration in the mix design. A reasonable correlation could be obtained between water absorption and specific gravity of both the coarse (Fig. 6a) and fine aggregate (Fig. 6b), although it was not sufficient to allow one to be estimated from the other. Porosity The porosity of the scoria particles was calculated using the following equation: npe/(1ce) where ep(gg w /g dry )P1 G is the apparent specific gravity g w is the density of water in g/cm 3 g dry is the dry density of scoria in g/cm 3 The calculated values ranged between 41 and 47%, with an average of 43% and standard deviation of 1.4%. These are relatively high compared with other light-weight aggregates. When the porosity values were plotted against the water absorption, no clear trend was observed (Fig. 7), supporting the contention that some of the pore spaces are not interconnected and could not be filled with water upon saturation. Fig. 7 Relationship between water absorption and porosity Bull Eng Geol Env (2000) 59 : Q Springer-Verlag 223

6 A. A. Sabtan 7 W. M. Shehata Heat insulation The heat insulation of the concrete prepared using the mix designs suggested by CIC (Moufti et al. 1999) was tested in Lee s apparatus. The average thermal conductivity of the concrete ranged between and W K 1 m 1 compared to the maximum average thermal conductivity for the prescribed density of the concrete of 0.43 W K 1 m 1 (ASTM C-332). The concrete produced therefore satisfies the ASTM requirements and can insulate heat 5 to 7 times better than the quartz sand concrete. Fig. 8 Pozzolanic activity of different scoria deposits. (After Moufti et al. 1998) Pozzolanic activity The pozzolanic activity of the scoria in the four locations was tested using the Italian Standards (Italian Chemical Society 1954) and reported by Moufti et al. (1998). The results of the tested samples fall below the lime solubility isotherm, indicating that all the scoria deposits are pozzolanically active (Fig. 8). Concrete properties The concrete properties were reported by Moufti et al. (1998, 1999) and are summarized as follows: Concrete strength Four mix designs were prepared and tested by Moufti et al. (1998, 1999). Three mixes were prepared according to the specifications provided by CIC with various percentages of fine scoria aggregate in addition to additives such as silica fume and Cico Fluid FG, while the fourth mix was prepared based on the weight method of Neville (1981) and using silica sand. The minimum average uniaxial compressive strength of the first three mixes was 35.8 MPa, satisfying the minimum required strength of 28 MPa for structural concrete (ASTM C-330). The fourth mix yielded an unacceptable average strength of 22.4 MPa. Splitting strength The splitting strength was performed only on the concrete prepared from the fourth mix. The average splitting tensile strength (Moufti et al. 1998) is reported as 2.4 MPa, just above the 2.3-MPa minimum allowable tensile strength for structural concrete (ASTM C-330). However, as the tensile strength values ranged between 2.2 and 2.5 MPa, some of the values were below the acceptable limits. A comparison of the behaviour of the different mixes under compression indicated that the concrete prepared using the mix designs suggested by CIC would probably have given satisfactory results. Conclusions and recommendations The aggregate properties of the scoria in its natural condition suggest that it is generally suitable as a light-weight aggregate, satisfying most of the ASTM requirements for structural concrete, concrete for masonry units and insulating concrete. If the scoria is taken from a reasonable depth away from the contaminated ground surface material and is processed, it will satisfy the remaining requirements. These studies are of particular importance not only for Saudi Arabia but also for other areas of similar climatic regime and geology. In Saudi Arabia, the extensive occurrence of scoria, its potential uses as structural concrete, in the manufacture of masonry blocks and as a heat-insulating material make it a valuable economic resource. Acknowledgments The authors wish to extend their gratitude to King Abdulaziz University for its financial support of Project no. 417/201 and the Faculty of Earth Sciences for making its laboratories and field facilities available to the research team. The authors are also grateful to CIC for giving the research team access to its site and permitting them to use its facilities and equipment. The authors are thankful to Mr. M. Ghazal for his assistance in the laboratory testing programme. References Abdul Hafiz K, Tayeb O, Ghandurah R, Roobol J (1998) Economic evaluation of basaltic and its derivatives in the north of Harrat Rahat. Proc 5th Meeting of Saudi Society Earth Sciences, Dhahran, Oct, Abstr, p 24 American Society for Testing and Materials (1995) Annual book of ASTM standards: section 4 (construction). Vol (Concrete and aggregates). ASTM, Philadelphia, 764 pp British Standards Institution (1975) Methods for sampling and testing of mineral aggregates, sand and fillers: BS 812. BSI, London, pp Collis L, Fox RA (1985) Aggregates sand, gravel and crushed rock aggregates for construction purposes. Geol Soc Eng Geol Spec Publ 1, 220 pp FIP (1983) FIP manual of light weight aggregate concrete, 2nd edn. Surrey University Press, Glasgow, 259 pp Italian Chemical Society (1954) Proc Symp on Pozzolanas and Their Use. Ann Chim 44 : Bull Eng Geol Env (2000) 59 : Q Springer-Verlag

7 Engineering properties of scoria Kazi A, Al-Molki ME (1982) Empirical relationship between Los Angeles abrasion and aggregate impact value tests. Proc 4th Congr IAEG, vol VI, pp Moufti MR, Sabtan AA, El-Mahdy O, Shehata WM (1998) Geologic and engineering assessment of the pyroclastic deposits in the central part of Harrat Rahat. Final report of project 417/201 submitted to KAU. (Also presented at 5th Meeting of Saudi Society Earth Sciences, Dhahran, Oct, Abstr, p 25) Moufti MR, Sabtan AA, El-Mahdy O, Shehata WM (1999) Assessing of industrial utilization of scoria materials in central Harrat Rahat. Submitted for publication in Engineering Geology Neville AM (1981) Properties of concrete. Pitman, London, 774 pp Terzaghi K, Peck RL (1968) Soil mechanics in engineering practice. John Wiley, New York, 729 pp Bull Eng Geol Env (2000) 59 : Q Springer-Verlag 225

Aggregates for Concrete

Aggregates for Concrete Fine Aggregate Sand and/or crushed stone < 5 mm (0.2 in.) F.A. content usually 35% to 45% by mass or volume of total aggregate Coarse Aggregate Gravel and crushed stone 5 mm (0.2 in.) typically between