Strength of pozzolan soil blend in chemically improved lateritic soil for pavement base material purpose

Abstract Map of Umuahia locating Ohia and Olokoro. Map of Umuahia locating Ohia in zone A. Nigerpet laboratory UCS (a) and (b) CBR test setup. Conventional cements’ contribution to global warming, environmental depletion and associated hazards has been alarming in recent years. This results from the release of carbon (IV) oxide into the environment during construction activities. This is due to the fact that almost all construction activities ranging from building construction, road construction, airfield pavements, dikes, pools, overhead tanks, tunnels etc. utilize very high amount of cement, hence release considerable tons of carbon (IV) oxide into the atmosphere. Pavement constructions and its foundation materials belong to the group of structural members that utilize cement as binder material. The present work tried to evaluate the effect of the use of naturally occurring pozzolan (china clay) in nanostructured texture on weak lateritic soil used as pavement foundation improved with very small amount of cement. The goal was to see how much foundation construction can be efficiently laid with little or no cement. Basic material characterization tests were conducted in accordance with relevant standards. From the results of the preliminary examination, the test soil was identified as A-2-7 soil, according to American Association of State Highway and Transport Officials (AASHTO) classification system and well graded (GW) by the Universal Soil Classification System. The lateritic soil was also identified as highly plastic soil with high clay content. It has good dry density at an optimum moisture of 13%. A California bearing ratio of 14% was observed and unconfined compressive strength judged to be moderately consistent cured at 28 days. The pozzolan sample was pulverized and characterized for use as nanostructured geomaterials to serve as an ecofriendly binder devoid of carbon (IV) oxide emission. The specimens for the strength test were prepared with soil/pozzolan blend proportioned at 3, 6, 9, 12 and 15% by weight of treated solid. The specimens were cured and subjected to compressive strength test in accordance to AASHTO standard for pavement construction. The pozzolan variation improved the strength of the weak soil until at 9% where the strengthening reached its peak and started reducing with further increase. Cement proportion was fixed at 5% throughout the proportional variations of environmental friendly binder. The strength achieved at 9% and at 28 days curing time met the minimum requirement for a material to be utilized as a base layer material under the laboratory conditions. Hence, pozzolan materials occurring naturally at Umuahia, Nigeria, spanning through the length of Port Harcourt, Enugu Nigeria, expressway can replace ordinary Portland cement as a binder in pavement construction to achieve an ecofriendly highway structures. The utilization of chemical additives in the re-engineering of weak and expansive soils for use in construction works has been a common practice [23–29]. However, this practice has equally caused unequaled disaster on the area of dangerous emissions that not only affect our overall health as humans and to animals but also destroy the ecosystem [21–29, 34]. This is a worrisome situation in the world today as we faced with construction practices that make cement utilization a must. Ozone layer depletion as a result threatens the future of our planet, and human and animal lives are on the edge. Since the 21st century, the evolution of supplementary cementing materials has been on [6–8, 21–29, 34]. This is targeted at replacing the utilization of cement partially or wholly and its associated unhealthy and hazardous emissions. A research has shown that for one ton of ordinary cement used in any construction activity, an equivalent amount is also released into the environment [6–8, 21–29, 34]. Certain ash and powder materials from the direct combustion and crushing of solid waste have been utilized as geomaterials over the years [6–8, 21–29, 34]. Going forward is the formulation of geopolymer cements as a coupled material under the influence of alkali activation substances, which has also evolved over the years. However, soil is important in various engineering projects such as pavement construction, drainage systems, buildings, canals, retaining walls etc. Regular situation arises where the soils do not meet the requirement for use as foundation materials in line with relevant design and practice standards [6–8, 21–29, 34, 35]. The degree of success in each case may be attributed to the geotechnical characteristics of soil, design techniques, construction procedures, environmental factors and the nature of the service of the structure. In the earliest era, Nigeria consisted of uplifted continental land mass made up of basements [23–29, 34, 35]. This resulted in the formation of lateritic soil, which is relatively of good quality for road construction work. The level of decay of structural facilities calls for concern from various bodies and agencies. For instance, in the southeastern part of Nigeria, over 90% of the roads are in a state of decay and more worrisome is that the relevant agencies in the works and housing sections and government are not doing anything to save this deplorable situation [30, 33, 34]. Some of such roads are the following: Enugu–Port Harcourt highway spanning in about four states of the country, Umuahia–Uyo highway spanning in two states, Enugu–Nsukka highway spanning and hosting federal institutions and leading to the Northern part of the country, Enugu–Awka highway spanning in two states, Uturu–Abakiliki highway spanning in two states also, Umuahia–Ohafia highway, Umuahia–Owerri highway spanning in two states, Owerri–Port Harcourt highway connecting two states and many more. Worst of all is the Egunu–Port Harcourt highway, which is supposedly a dual carriageway connecting five southeastern states of Rivers, Abia, Imo, Ebonyi and Enugu. We all have a duty to save the environment and research works such as this are ongoing to proffer geoenvironment solutions. This research work has investigated into the stabilization potentials of naturally occurring pozzolanic soil, which is obtained at no cost from Umuahia [23–29, 34, 35]. While we have embraced the new trend in materials technology to alter and improve the geomaterial properties, we have also compared our findings with an earlier study carried out on this material. The field of nanotechnology gave us a platform to try new procedures of applying the pozzolanic soil to study its effect on the compressive strength of test lateritic soil as an additive. Nanotechnology is the science that uses and manipulates matter at nanoscales [23–29, 34, 35]. With this size, atoms and molecules work differently and provide a variety of surprising and interesting uses. Nanotechnology represents the design, production and application of materials at atomic, molecular and macro molecular scales, in order to produce new nanostructured materials [1, 3, 17, 18]. Also, nanomaterials are materials with one external dimension in the size range from ~1–100 nm while nanoparticles are small objects that behave as a whole unit with respect to its transport and properties and they are particles between 1 and 100 nm in size. One aspect having frequently been discussed in recent years is the question as to whether metal-based nanoparticles exert higher toxicity when compared to water-soluble metallic compounds or microscale particles of the same metallic content. The benefits of pozzolan utilization in cement and concrete are 3-fold [1, 2, 4, 5, 14, 23–29, 34, 35]. First, the economic gain obtained by replacing a substantial part of the ordinary cement by cheaper, pollution-free, natural pozzolan material and industrial by-products. Second is the lowering of the blended cement production and consequently reducing the associated carbon (IV) emission during its production and utilization [9, 10, 15, 16]. A third advantage is the increased durability of the end product. Additionally, the increased blending of pozzolan with ordinary cement is of limited interference in the conventional production process and offers the opportunity to create value by converting large amounts of industrial and societal waste into durable construction materials. Soil stabilization refers to the sum total of the procedure in which weak or expansive test soil and a cementitious material (binder) or other chemical or non-chemical materials are mixed to improve the engineering properties of the test soil or the unique use of a natural soil to improve its properties [2]. Soil stabilization techniques for road construction are used in most part of the world, although circumstance and the reasons for resorting to stabilization vary considerably [19, 20, 32]. Soil stabilization has widely been recommended for developing countries for various elements of their pavement construction especially Nigeria. Nano technological achievements provided a modern approach in geotechnics. Each field of science had a specific definition for nanotechnology, and the National Nanotechnology Initiative provided a comprehensive definition of nanotechnology as the control, comprehension and reformation of material based on the hierarchy of nanometers to develop matter with essentially new uses and a new constitution with improved reactive surface. Years later, geotechnical experts have keyed into this technology to develop ideas and procedures for using this tech to enhance the environment through engineering soil improvements and stabilization. This improves the bonding between stabilization additives or admixtures and stabilized engineering soil materials. Therefore, it becomes more reactive and potentially suitable for improving the properties of soil for various applications [3, 30,33]. Meanwhile, Norazlan et al. [32] was stated by using a small percentage of nanoparticle of kaolin to influence the basic properties and engineering of kaolin. There are increased research and development in nanoparticles that have been used as filler or additives for various desired effects. However, the specific objectives of this exercise were (i) to investigate the effect of nanostructured natural pozzolan soil on the compressive strength of stabilized lateritic soil and (ii) to proffer its use to remedy the dilapidated roads in the southeastern part of Nigeria neglected by government. Lateritic soil sample used for this study was collected from a borrow pit geographically located at Olokoro, between latitude of 05°28′36.700″ north and longitude 07°32′23.170″ east from a depth of 2 m, a distance of 5 km along Ubakala road from Ishi Court Umuahia, the Abia state capital in Nigeria (Google Map) as presented in Figure 1. The sample collected was in solid state and reddish brown in color. The soil obtained from this location was air dried in trays for 6 days, after which the soil was gently crushed with plastic pestle. The dried soil was further pulverized, using rubber covered pestle in the tray and sieve characterization with orderly arranged British Standard sieves to [11] 4.36 mm, 2.36 mm, 1.18 mm, 300 μm, 212 μm, 150 μm and 75 μm. On the other hand, the pozzolan soil sample (kaolin clay) used for this investigation was collected from Ohia adjacent to the Mechanic village, on Enugu–Port Harcourt highway in Umuahia South Local Government Area of Abia State, Nigeria, as geographically presented in Figure 2. The sample was collected in a sack bag and was air dried to eliminate the moisture in it for 7 days. It was then crushed to powder with core cutter and bulk density mold. Subsequently, the powder was completely pulverized and passed through 200 nm sieve and stored for use. The material was also subjected to ultra violet visual spectrophotometric characterization to determine the variation of absorbance behavior and wavelength. Ordinary Portland (OP) cement, which satisfied the material condition in accordance with American Standard for Testing and Materials [4], was used as a secondary binder. A constant percentage of 5% was maintained throughout the experiment. The proportioning and blending of the treated geomaterials were done with 3, 6, 9, 12 and 15% pozzolan by weight of solid. The natural pozzolan material was utilized as the primary binder. The following fundamental tests were conducted in accordance with BS 1377-2 [11]; BS 5930 [13]; Nigerian General Specification/Federal Ministry of Works and Housing [31]; sieve analysis test, compaction test (standard Proctor test), California bearing ratio test (CBR), Atterberg limit test (Casagrande apparatus), unconfined compressive strength (UCS) test, specific gravity test and chemical composition test on the natural soil sample and results were obtained. This was conducted under laboratory conditions in a Geotechnical Engineering Laboratory, Uyo, Akwa Ibom State, Nigeria, on the sample with admixture proportions of 3, 6, 9, 12 and 15% in accordance with BS 1924-2 [12] and Nigerian General Specification/Federal Ministry of Works and Housing [31], and the experimental setup is as presented in Figure 3a and b. This is a strength test that satisfies coupled geomaterials ability to withstand compressive and cyclic loads. Particle size distribution curve of the lateritic soil sample. Variation of absorbance against wavelength for the lateritic soil using ultra violet visual spectrophotometer at 25°C. The results of the preliminary investigation carried out on the test soil are presented in Table 1. It can be deduced from the table that the test soil has a plasticity index (PI) of 21.85%, which is greater than 17%, a condition that qualifies soils to be judged as highly plastic and that condition satisfies that the test lateritic soil was a highly plastic soil. Also, the PI falls between 20 and 35%, a condition for high swelling potential, and between 25% and 41%, a condition for a high degree of expansion according to the proposition by Gopal and Rao [20]. Secondly, from the consistency limit tests (Atterberg limits) that the soil relative consistency and liquidity index, which are 1.69% (greater than 1) and 0.91% (less than 1), respectively, show that the soil is in a semi-solid or solid state, very stiff and plastic according to the results of Gopal and Rao [20]. This went on to establish that the materials satisfy to be utilized as a subgrade material for pavement foundation purposes. Thirdly, the test soil was classified as A-2-7 soil using the American Association of State Highway and Transport Officials (AASHTO) soil classification system, classified as well graded, (GW) soil by using the Universal Soil Classification System (USCS), with a group index of 0 and of silty, clayey gravel and sand material according to the findings of Gopal and Rao [20]. Fourthly, the test soil had optimum moisture content (OMC) of 13% and maximum dry density (MDD) of 1.84 g/cm3 from the compaction experimentation. Fifth, the soil had UCS of 230.77 kN/m2 at 28 days curing time, which falls between 200 and 400 kN/m2, a condition for soils of very stiff consistency with respect to UCS, which satisfies the material condition for use as subgrade material [20, 30,31, 34]. And lastly, a CBR of 14% was observed from test result, which makes it good for the subgrade material also [31]. Figures 4 and 5 and Table 1 also presented that the soil is a well-graded soil with coefficient of curvature) (Cc) equals 0.09, coefficient of uniformity (Cu) equals 10 and possesses an absorbance of 1.154 nm at the wavelength of 800 cm. Effect of nanostructured pozzolan blend on UCS of soil. From the effect of pozzolan additives on the UCS of the stabilized lateritic soil presented in Table 2 and Figure 6, it can be observed that the addition of pozzolan as a primary binder to the cemented soil improved the strength of the sample from basic 194.26 kN/m2 at control experiment to 192.8 kN/m2 at 3% by weight, 273.1 kN/m2 at 6% by weight, 286.5 kN/m2 at 9% by weight, 300.4 kN/m2 at 12% by weight and 341.6 kN/m2 at 15% by weight at 7 days curing period. This shows that at the initial curing period of 7 days, the cementing admixture improved the strength of the treated soil consistently. However, the strength improvement at 14 days curing period though was good but was not consistent. It recorded the maximum compressive strength of 357 kN/m2 at 15% by weight proportion of pozzolan. It reduced very undesirably at 9% by weight addition of pozzolan. While the strength improvement at 28 days curing time recorded a maximum of 369.9kN/m2 at 9% by weight proportion of pozzolan, the stabilized soil strength dropped with further addition of pozzolan of 12% and 15% within this curing period [23, 25]. This proved to be the best exercise though and the proportion to be used in the improvement of the compressive strength of Olokoro lateritic soil since civil facilities like roads are constructed for use as long-term projects. It is important to note the reasons behind the inconsistent results as contained in Table 2. It is possible that the addition of such naturally occurring material like pozzolan could affect the already known performance of OP cement, which served as a secondary binder [24, 30,34]. This factor makes the studied mixture to lose strength after some days of curing and subsequently regained even more strength after a longer period. The initial strength gain by cement we know is spontaneous and rapid and could also be lost by the reaction between cement and material admixtures, hence the inconsistent behavior we experienced in the above results. From the foregoing, it can be concluded as follows: That pozzolan (kaolin clay) is a good admixture in the stabilization of expansive lateritic soils. This is for improvement of the compressive strength of the engineering soil properties for use as base material in pavement construction. That this material additive should be used at 9% by weight of solid proportion to achieve the highest strength for a long-term use of the pavement facility and the relevant ministries of works and housing should make use of the naturally occurring pozzolan soil for a cost-effective facilities construction and rehabilitation because of its cementitious properties. However, the utilization of 15% by weight pozzolan blend in the treatment of weak soils meets the standard for a material’s use as base material in pavement construction under the laboratory condition also. However, the replacement of ordinary cement with an ecofriendly binder reduced the risk of carbon (IV) oxide emission the environment may have suffered with the utilization of 100% cement. Hence, it is proposed that civil engineering construction activities should make use of materials with less or no disastrous emissions like in the case of pozzolan utilization to help save our planet from the rampaging and fast encroaching effects of global warming resulting from these unhealthy construction practices.

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