1. Introduction

2. Materials and methods

3. Results and discussion

4. Conclusions

Abstract

This study aims at investigating the possibility of using smectite clay waste, generated during the oil bleaching process as an additive for Portland cement. The smectite clay waste consists of montmorillonite, quartz, anorthite, calcium sulfate, and amorphous phase. For the regeneration of this waste, the extraction with hexane and thermal method were chosen. The results showed that the extraction of smectite clay waste with hexane significantly increased the pozzolanic activity of this waste; however, the extracted additive prolonged the induction period of Portland cement hydration, slowing down initial cement hydration, and reduced the compressive strength of Portland cement samples.

The thermal activation method achieves the best results by calcining smectite clay waste at 600 °C. The calcined additive indicated the strong pozzolanic activity. However, this phenomenon is associated with the formation of the amorphous phase by activating the smectite clay with the sulfuric acid rather than the degradation of the clay minerals during the combustion. The calcined smectite clay waste (CSCW) accelerates the hydration of calcium silicates in the second period of the exothermic reaction. The results of the investigation showed that in samples with the CSCW additive proceed the intense pozzolanic reaction, which can be clearly identified after 28 days of hydration. Up to 15 wt% of the Portland cement can be replaced by the smectite clay waste additive calcined at 600 °C without reducing the compressive strength of Portland cement samples.

Introduction

Nowadays one of the most current issues is the environmental pollution caused by industrial waste, which is being produced by large-scale production in various industries. Only a small part of the industrial waste is recycled and its application in other industries is highly important. Various studies have shown [1-5] that some industrial waste can be used by replacing a part of the clinker in cements or a part of the cement in concrete. In this case, when the waste is used as an additive for 32 binding materials, not only the pollution issue is solved but also the cost of Portland cement or concrete is decreased.

Oil bleaching is one of the processes applied in oil industry during which the impurities that add colour to the oil are removed and oil is purified from carotenoids, peroxides, chlorophyll, etc. Oils are bleached using a powdered, surfactant materials, which are called bleaching earths. Bleaching earths can composed of up to different types of clay minerals, such as smectite, bentonite, attapulgite and sepiolite. The bleaching process is carried out under vacuum, with temperature in the range of 80-120 °C and contact time ranging from 20-40 min. The dosage of bleaching earth usual is 0.5-2 % by weight. After bleaching, the mix of clay and oil are separated by the vacuum filtration into two phases: oil and clay waste. As a consequence, the oily clay becomes hardly recycled waste. Market demand for activated bleaching earth was predicted to rise to ~9M/year tones until 2022, therefore, the amount of waste produced through the edible oil bleaching process, is considerable [6].

The bearing capacity of foundations on soft clays under undrained conditions has been computed with inclusion of (i) a single vertical granular trench below a strip footing and (ii) a granular column placed below a circular footing. A lower bound plane strain and axisymmetric limit analysis, in conjunction with finite elements and an optimization procedure, has been used. The efficiency factor (n) has been determined by varying Bt/Bf; where (i) Bt = diameter of the column (width of the trench) and (ii) Bf = diameter of the circular footing (width of the strip footing). The effect of (i) the depth (D) of the column (trench) and (ii) the angle of internal friction (/) of the column (trench) material has been explored for a wide range of cu/(cBf); cu and c imply undrained cohesion and the unit weight of the clay mass, respectively. Factor n increased quite significantly with increases in Bt/Bf and D/Bf. Factor n improved further with (i) increases in / and (ii) decreases in cu/(cBf).

Introduction

A number of investigations, that examined the improvement in the bearing capacity of foundations by the insertion of granular trenches and columns, have been reported in literature. The studies are based on (i) analytical approaches (Madhav and Vitkar, 1978; Bouassida and Hadhri, 1995; Bouassida et al., 1995), (ii) elasto-plastic finite element analyses (Schweiger and Pande, 1986; Mitchell, 1985), and (iii) numerical lower and upper bound finite element limit analyses (Bouassida et al., 2015). Series of small-scale model experiments (Hamed, 1986; Nazir and Azzam, 2010; Bouassida and Porbaha, 2004) and full-scale field tests (Mitchell, 1981, 1985; Stuedlein and Holtz, 2012) have been carried out by a few researchers. These different model and field tests revealed that the bearing capacity of foundations can be increased quite significantly with an increase in the depth of the granular trench. In the present paper, the aim is to determine the bearing capacity of both strip and circular footings, placed on soft to medium soft clays reinforced with a single granular trench and column, respectively, by using the lower bound limit analysis with finite elements and the optimization principle.

Introduction

Seismic performance evaluation of soil-structure systems built on very soft high plasticity clays is a complex problem, especially when expected changes in effective stresses during the economic life of the structure due to dissipation of excess pore pressure caused by the building gravity loads and regional subsidence are very large. These changes in effective stresses lead, in turn, to large settlements. This is particularly important in urban areas located in highly compressible clays, such as Mexico City, where the settlement rate of regional subsidence reaches about 10 cm/year in average, but can go as large as 35 cm/year in some areas. Thus, it is common to have ground settlements ranging from 40 to 90 cm, due to load consolidation, and around several meters due to regional subsidence [1]. These settlements produce changes in both soil profile configuration (i.e. layer thickness and geometry), as well as dynamic properties, such as shear wave velocity distribution with depth and modulus degradation and damping curves. These factors impact the seismic response of the soil-structure system. The effect of dynamic properties changes on the seismic response of sites located in soft clay, has been only marginally studied by other researches [2–5], finding that the variation of shear wave velocities and modulus degradation and damping curves with effective confining stresses can modify significantly the computed response. Nevertheless, the impact of these variations in the seismic performance of soilstructure systems has not been addressed, neither the effect of changes in the soil profile configuration after several meters of sinking. These effects however, can drastically modify both free field, near field and structural response over time. This paper presents a numerical study of the seismic response of a conventional five-story building supported by a partially compensated box foundation built in highly compressible soft clay, considering these effects. Three-dimensional finite difference models were developed with the software FLAC3D. Initially, the evolution of effective stresses with the pore pressure was established based on in-situ piezometer measurements, and laboratory data. Then, variations in dynamic properties were taken into account based on a series of resonant column tests conducted for several mean effective consolidation stresses and a suspension logging test. The static behavior of the soil-structure system was assessed. The free field model response was calibrated for moderate to strong level of shaking (i.e. return periods of 125 and 250 years, respectively) comparing the fully nonlinear analyses results with equivalent linear analyses carried out with the program SHAKE [6]. Finally, the seismic performance of the soilstructure system was studied to evaluate the impact of the changes on dynamic properties and layering configuration on the seismic response, considering an extreme subduction event associated to a 2475 years return period. Insight was gained regarding the complexity of the interplay of the effective stress history, and static and seismic soil-structure performance during an extreme earthquake.

This paper presents the results of four large-scale shallow foundation tests on soft estuarine clay carried out at the Australian National Field Testing Facility (NFTF), near Ballina, NSW, established as part of the activities of the Centre of Excellence for Geotechnical Science and Engineering (CGSE). Two rigid square pad foundations were loaded concentrically to failure in an unconsolidated and undrained condition (UU1 and UU2). Another two foundations were loaded with 30% and 50% of the measured UU failure load and allowed to fully consolidate before being brought to failure under undrained vertical concentric loads (CU1 and CU2). In this paper, the foundation response is analysed in conjunction with high quality site investigation data. An international shallow foundation prediction exercise was run in conjunction with these field tests to assess the current state of practice for predicting the undrained load-settlement response and ultimate capacity of shallow foundations. The outcomes of the prediction exercise are presented in a companion paper in this special issue [1]. Results of large-scale foundation tests on soft clay under vertical centric loading are sparse in the literature, and most notably include those carried out at the UK’s national soft soil test site, in Bothkennar, Scotland [2,3]. The Bothkennar site was extensively characterised as part of the research initiative [4]. The philosophy of the NFTF, at which the tests presented in this paper were carried out, was based on the Bothkennar exemplar. Similarities also exist in terms of the site conditions and foundation geometry. The Bothkennar site comprised a weathered crust to around 2 m depth below ground level overlying clay and silt that were deposited under marine or estuarine conditions with the summer water table 0.9 m below ground level [2]. The undrained shear strength within the clay/silt layer was also similar at the two sites. At Bothkennar, five rigid square pad foundations, of the same shape and similar size were tested over a period of 11 years enabling insights into the effect of long term preloading on foundation bearing capacity. However, some notable differences preclude direct comparison of outcomes from the Bothkennar tests and those from the NFTF. For example, the Bothkennar foundations are cast within the crust layer rather than at the top of the underlying estuarine clay layer as at the NFTF and the rate of loading to failure of the foundations at Bothkennar was two orders of magnitude slower than those at the NFTF, while the consolidation period between sets of tests was an order of magnitude greater. The experimental approach adopted for the Bothkennar field tests was drawn from earlier work of field tests on clays [5–9]. The shallow foundation construction details and observed performance, as presented in this paper, are freely available in digital form through www.geocalcs.com/datamap [10]. The site data and results from all the laboratory and in situ testing are also available through the online platform.

The piled-raft is a geotechnical foundation consisting of the three elements raft, piles and soil. Burland (1977) proposed that the piles can be used to reduce the settlement of the raft foundation. In piled-raft foundation, the total load of the superstructure is partly carried by the piles and the raft. The distribution of total load among the piles, raft and soil depends on their relative stiffnesses. Based on the dimensions of the raft and piles, the piled-raft has been classified as a small piled-raft (Br/Lp < 1) and large piled-raft (Br/Lp > 1) (Viggiani, 2001; Sanctis and Mandolini, 2006; Mandolini et al., 2013). In a small piled-raft, the flexural stiffness of the raft is usually high and the differential settlement does not represent a problem. Here, the primary reason to add the piles is to achieve a sufficient factor of safety against the bearing failure. However, in a large piled-raft, piles are added essentially to reduce the settlement. Poulos (2001) indicated that the 3-D numerical modeling is the most reliable method for the analysis of the piled-raft foundation in a clay soils. The maximum settlement, differential settlement, raft bending moments and shear force, axial loads and pile bending moments are considered as crucial parameter for optimum design of piled-raft foundation. Several researchers have been investigated the settlement (Prakoso and Kulhawy, 2001; Cho et al., 2012; Sinha and Hanna, 2016) and bearing behavior (Reul, 2004; Sanctis and Mandolini, 2006; Lee et al., 2010) of a piled-raft foundation on clay soils by numerical modeling. Oh et al. (2008) conducted a study on the piled-raft foundation in sandy soil by numerical modeling. They reported that with increase in raft thickness and pile spacing, the bending moment of the piled-raft increased. The different design aspects of the piled-raft foundation have been reported by Seo et al. (2003), and Reul and Randolph (2004). Ghalesari et al. (2015) suggested that the piled-raft foundation can be adopted as offshore foundation to reduce the settlement and to enhance the bearing capacity of the foundation. Furthermore, Poulos and Devdas (2005), Poulos and Bunce (2008), Poulos et al. (2011), Rabiei and Choobbasti (2016) indicated that the piled-raft can be used as an effective and economic foundation alternative for tall buildings to control the settlement and to enhance the bearing capacities. In addition to this, Nguyen et al. (2014) conducted a parametric study of large piled-raft foundations in sandy soil through finite element modeling. They indicated that the concentrated pile arrangement method can help to considerably reduce the settlements and bending moments of the raft. However, very few parametric studies by means of numerical modeling have been reported for the large piled-raft foundation on a clay soils. Therefore, the effect of different parameters on large piled-raft foundation needs to be investigated. The intended large piled-raft foundation can be used for the construction of residential or commercial buildings situated near onshore line where mostly undrained conditions prevail.

Since the Niigata and Alaska earthquakes in 1964, many researches have been carried out on soil liquefaction. Soil seismic liquefaction occurs due to the increase in excess pore water pressure of soil. It will cause huge disasters to human populations (Juang and Li 2007; Huang and Jiang 2010; Bhattacharya et al. 2011; Huang and Yu 2013). In studies of soil liquefaction, fine and ultrafine particles play an important role, because these small particles influence soil instability (Abedi and Yasrobi 2010), static shear strength (Yang and Wei 2012), and cyclic shear strength (Beroya et al. 2009). The size of small particles is about nano- and microscale (Otterstedt and Brandreth 1998), and it incorporates three different types of particles (from 1 nm to 75 lm) based on the review of this problem. In particular, the non-low plastic fines, clay particles, and ultrafine particles were considered as distinct categories because of their very different size and properties. The specific definition of particles size will be introduced in Sect. 2. The effects of fine particles on soil liquefaction have been known since the 1970s. A Chinese liquefaction susceptibility criterion was first proposed by Wang (1979). This famous criterion considers the effects of fine particles based on the observed failures following the 1975 Haicheng and 1976 Tangshan earthquakes. Seed and Idriss (1982) modified this ‘‘Chinese criterion,’’ pointing out that soil types and clay content (Cc) are crucial to liquefaction, since soils with clay fines (\5 lm) of more than 15% will not be liquefied. Seed et al. (1985) also found that fine particles (\75 lm) influence standard penetration test (SPT) blow counts (Fig. 1), with liquefaction resistance increasing with increasing fine content (Fc). Tokinatsu and Yoshimi (1983) came to the same conclusion for soils containing clay particles. Although it believes that the soils with high Fc or Cc will not liquefy, there are many cases of soils with high Cc that were reported to have liquefied during strong earthquakes (Tan et al. 2013). For example, soils containing 19% Cc were found to be liquefied in the Chi-Chi earthquake (Hwang and Yang 2001), as well as the Marmara (Turkey) earthquake (Bol et al. 2010). This has led to ongoing discussion of the roles of small particles in liquefaction. More recently, scholars have found that ultrafine particles (e.g., nano bentonite) inhibit the generation of pore water pressure, and those particles can be used to mitigate soil liquefaction (Gratchev et al. 2007; El Mohtar et al. 2008, 2013). In addition, there are many indices used to evaluate soil liquefaction resistance for soils containing clay particles, including Cc (Ghahremani and Ghalandarzadeh 2006), plasticity index (PI) (Boulanger and Idriss 2006), as well as the content of specific clay minerals (Beroya et al. 2009). In this paper, the effects of small particles on the liquefaction resistance were reviewed based on three different particles. In addition, we outline the research challenges related to working on soil liquefaction of soils containing small particles.

Diatomite (DM) is a low-cost, environmentally friendly, and natural microstructured/nanostructured material derived from sedimentary silica. It has cylindrical and plate morphologies with well-developed mesoporous and/or macroporous structures.1–6 The highly developed pore structure, low density, and high surface area of DM results in it having a number of industrial applications, including as filtration media for various inorganic and organic chemicals and absorbents.2–7 Although DM is not frequently used as a novel papermaking filler, its use has become an increasingly important research area.4–10 Compared with traditional papermaking fillers, DM as a kind of novel papermaking filler has many advantages; these include its light weight, high porosity, low wire wear, and good adaptability. In the modern papermaking process, great changes in fibrous raw materials have taken place, and deinked pulp and high yield pulp are used extensively. As the closure degree of white water increases, the accumulation of anionic trash in paper furnish causes a lot of problems to wire operation and sheet properties.11–19 Anionic trash is one of the popular names used to describe a wide range of dissolved anionic polymeric and colloidal materials. Another common name for this is DCSs, which stands for dissolved and colloidal substances. At present, the main methods of eliminating anionic trash are chemical and biological methods.5–9,20–26 The chemical fixation method uses anionic trash catchers (ATCs), such as polyethyleneimine (PEI) and poly(aluminum chloride), to remove anionic trash and neutralize the electronegativity of DCSs. ATCs have some beneficial effects on the elimination of anionic trash, but they may also cause new problems. They may have a negative impact on the effectiveness of cationic additives and may be unable to firmly anchor anionic trash onto pulp fibers. Nowadays, there have been plenty of studies on the application of ATCs in anionic trash elimination.2–9,20–31 However, the use of ATCs to modify the DM surface and the application of the modified product to the papermaking process have not been reported.

مقاله سال 2016