Stabilization of Highly Expansive Moreland Clay ...

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Stabilization of Highly Expansive Moreland Clay Using Class-C Fly Ash Geopolymer (CFAG)

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Md Adnan Khan, Ph.D., M.ASCE1; Jay X. Wang, Ph.D., P.E., M.ASCE2; and Debojit Sarker3 1

Shannon & Wilson, Inc., 400 N. 34th St., Suite 110, Seattle, WA 98103. E-mail: [email protected] 2 Programs of Civil Engineering and Construction Engineering Technology, Louisiana Tech Univ., Ruston, LA 71272. E-mail: [email protected] 3 Programs of Civil Engineering and Construction Engineering Technology, Louisiana Tech Univ., Ruston, LA 71272. E-mail: [email protected] Abstract Volume change behavior of the Moreland clay, which is full of montmorillonite mineral, is one of the major causes of building and pavement damage in northern Louisiana. Using class C fly ash geopolymer (CFAG) to stabilize expansive soil is not new and becoming more accepted in the industry nowadays. However, stabilizing the Moreland clay using CFAG has never been extensively studied or well documented. In this research, the Moreland clay stabilization with CFAG (5, 10, and 20%) was studied and then its performance was compared with a traditional soil stabilizer which is cement (10%). Consolidation tests were performed 7, 14, and 30 days after the samples were prepared. From the compression index (CC) and swelling index (CS) values it was concluded that even though cement is by far the best soil stabilizer the application of a higher percentage of CFAG, a satisfactory level of soil stabilization can be achieved. Introduction Expansive soil is a type of clayey soil that undergoes large changes in volume due to fluctuation of moisture content (Al-Homoud et al. 1995; Chen 1975; Erzin and Erol 2007; Groenevelt and Grant 2004; Khan 2017; Khan and Wang 2017; Khan et al. 2017a; Khan et al. 2017b; Ng et al. 2003; Nwaiwu and Nuhu 2006; Wang et al. 2017; Zhan et al. 2007). The change in volume is one of the most common causes of pavement and/or building distresses. Every clayey soil shows somewhat volume change associated with a moisture content change. However expansive soil, which is full of montmorillonite clay mineral, shows a significant volume change (Çokça 2001). Jones and Holtz (1973) first quantified the extent of damage on structures due to expansive soil and estimated that in the USA the damage was about $2.3 billion/yr in 1973, which exceeded the combined damage by earthquakes, hurricanes and floods. Later, Krohn and Slosson (1980) quantified the annual damage by expansive soil, which was around $7 billion USD in 1980. According to Snethen (1986) one fifth of American population lived on expansive soil. The total annual damage by expansive soil in USA today well exceeds $15 billion and in spite of this alarming damage expansive soil is still excluded from the Federal Emergency

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Management Agency’s (FEMA) list of the costliest natural disasters (Buhler and Cerato 2007). Fredlund et al. (2012) explained there are two main reasons behind the lack of significant development for expansive soil research: (1) insufficient science with theoretical background because the stress condition and mechanics involved in an unsaturated expansive soil are not properly understood and (2) insufficient financial recovery for engineers because the possible liability to an engineer is often large relative to the financial remuneration, especially with regard to expansive soil. Expansive soil swells when it is wetted and shrinks when dried, and thus it leads to cracking and buckling of pavements, sidewalks, slab on ground, driveways, pipelines and foundations (Nalbantoğlu 2004). Figure 1 shows typical longitudinal cracks that occur in pavements resting on expansive soil.

Figure 1. Subgrade Volume Change-Induced Pavement Longitudinal Cracks Most common technologies that are employed to alleviate the harmful effects of expansive soils are: 1) Soil Cap- using the cut and fill method to replace expansive soil with nonexpansive soil up to a certain depth; 2) Drainage- providing adequate draining around the structures to promote a rapid runoff; 3) Use of exterior slab- exterior slabs may get damaged by the subgrade volume change but its more accessible and less expensive to repair. Most importantly it will prevent moisture to go underneath the floor; 4) Design of slab on groundincreasing the thickness of slab on ground and reinforcing it to resist the subgrade movementinduced stress; 5) Special slab on ground using waffle mat system will allow the soil to slide in to the waffle boxes when it swells; 6) Geosynthetics- placing geosynthetics (i.e., geotextile and geogrid) inside the subgrade soil; 7) Mechanical stabilization- compacting the subgrade soil will reduce expansive soil’s seasonal movement and 8) Admixture stabilization- Different pozzolanic agent (i.e., cement, lime and fly ash) and industrial waste (i.e., dredged mud, slag, sludge ash, rice husk, crushed concrete powder, PC-8, calcium carbide residue and bagasse fiber) can be used to stabilize expansive soil (Al-Malack et al. 2016; Correia and Rasteiro 2016; Dang et al. 2016; Du et al. 2016; Etim et al. 2017; Jaditager and Sivakugan 2017; Jahandari et al. 2017; Kumar Yadav et al. 2017; Miao et al. 2017; Nelson et al. 2015; Seco et al. 2017). In this paper, stabilization of the Moreland clay with class C fly ash-based geopolymer (CFAG) is investigated. CFAG has properties similar to ordinary portland cement (OPC) which are: high strength and strength-gain rate; superior resistance to corrosion, heat and chemical

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attack and low permeability, with a lesser carbon footprint than OPC (Davidovits 1993). According to Davidovits (1991), for every ton of OPC produced, one ton of carbon dioxide is released into the atmosphere, making it a serious concern to the global greenhouse gas effect. One of the impressive things about geopolymer is that it can be produced either by naturally occurring raw materials (i.e., clay and mica) or by making use of industrial byproducts (i.e., fly ash and rice husk ash). One of the major problems is lack of awareness of the CFAG advantages over OPC. Where OPC is used so widely, geopolymer is still perceived to be more of a laboratory product (Islam 2013). Understanding the benefit of geopolymer compared to traditional stabilizer (i.e., cement and lime), the department of transportation (DOT) in various states (i.e., Texas, Oklahoma, Indiana and Arkansas) already accepted the direct use of fly ash or fly ash combined with cement or lime to stabilize expansive soil (AHTD 2014; INDOT 2008; ODOT 2009; TxDOT 2005a; TxDOT 2005b). After a review of the 2006 and 2016 Louisiana Department of Transportation and Development (LADOTD) standard specification of roads and bridges (LADOTD 2006; LADOTD 2016), it can be concluded that 1) there is no specification for using fly ash as a soil stabilizer, and 2) there is no stabilization standard for soils with a plasticity index (PI) higher than 35 (i.e., Moreland clay). In many places of northern Louisiana, there is an abundant presence of expansive soils with high groundwater table (GWT) (Dhakal 2009). Most of the expansive soils in northern Louisiana is the Moreland clay which has a high plasticity index (Khan 2017). Louisiana Department of Transportation and Development (LADOTD)/Louisiana Transportation Research Center (LTRC) have conducted and sponsored a small limited number of research projects on expansive soil, but stabilization of the Moreland clay has still not been well addressed or corresponding research has not been well documented in Louisiana (Abu-Farsakh et al. 2012; Abu-Farsakh and Nazzal 2009; Melancon 1979; Rupnow et al. 2011; Wang 2002; Wu et al. 2011). This research will help understand the Moreland clay’s swell-shrink behavior in depth and its stabilization with CFAG. 2. CFAG Chemistry CFAG is basically class-C fly ash in the presence of an activator solution. Once fly ash and activator solution are mixed, it creates geopolymeric chains, which is referred to as geopolymerization. The empirical formula developed by Davidovits (1991) for aluminosilicate can be written as Mn{-(SiO2)z-AlO2)n.wH2O where M can be any number of cation (i.e., Na+, K+, Ca++ , Ba++, NH4+, H3O+), and n is the degree of polymerization. The letter “Z” represents 1, 2, or 3, determining the resulting geopolymer net. For the case of Z=1, the net will be of the polysialate type. If Z=2, the net will be a poly(sialate-siloxo), and if Z=3, the net will be a poly(sialate- disiloxo) (Islam 2013). Figure 2 presents the structural model proposed by Davidovits (1993). Scientists indicated that there are three main steps of geopolymerization (Davidovits 1991; Duxson et al. 2007; Islam 2013; Mo et al. 2014; Provis and van Deventer 2007; Silva et al. 2007). These three steps typically overlap each other under thermal curing and they are hard to be recognized in the reaction process. The three steps are: 1) Dissolution of silicon and aluminum species from the source material through the action of a highly alkaline solution; 2) Transportation of species and formation of monomers and 3) Polycondensation and growth of polymeric structures, resulting in the hardening of the material.

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3. The Moreland Clay According to the United States Department of Agriculture (USDA) soil taxonomy classification, the Moreland clay is very fine, smectitic, thermic Oxyaquic Hapluderts, expansive and considered as a very poor construction and road fill material (USDA 2013). Using the “soil series extent mapping tool,” the Moreland clay presence in the USA is plotted in (Figure 3). From Figure 3, it can be concluded that 4,872,710 acres of the Moreland clay spreads over Louisiana, Arkansas and Oklahoma, with most of it present in Louisiana. After breaking the total acres down by individual county/parish, it is found that Caddo Parish (43,580 acres) and Bossier Parish (31,781 acres) have the fourth and fifth highest acres of the Moreland clay, whereas Avoyelles parish (116,293 acres) has the most acres of the Moreland clay (Khan 2017). Figure 4a shows the foundation damage of a church located in Bossier City, LA and Figure 4b shows longitudinal cracks found on a pavement at Tacoma Blvd. in Caddo Parish, LA due to the expansive subgrade.

Figure 2. Structural Model of Geopolymer Proposed by Davidovits (1993)

Figure 3. Moreland Clay Map of USA © ASCE IFCEE 2018


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(a)

(b) Figure 4. (a) Structural Damage in Bossier City and (b) Pavement Cracked in Caddo Parish Due to Moreland Clay Table 1. A Summary of the Soil Properties of the Moreland Clay (Khan 2017; Khan et al. 2017a; Khan et al. 2017b) Soil Properties Value Soil Properties Value Fat Clay Saturated unit weight (w=52%), USCS soil classification 19.70 kN/m³ (CH) Field unit weight (w=32%), 0.075 mm passing (%) 99 17.11 kN/m³ Specific Gravity, Gs 2.75 Compression Index, Cc 0.36 Activity of clay, Ac 1.3 0.11 Swell Index, Cs Liquid limit, LL 79 Corrected swelling pressure, kPa 180 Plastic limit, PL 28 Expansion Index, EI 101 Direct shear test (Saturated cʹ = 23 kPa, Plasticity Index, PI 51 condition) ϕʹ = 18.80 Avg. initial void ratio, e0 1.27 Fitting parameter, k 2.33 Avg. Field Moisture content (%) 32 Shrink swell modulus 0.45 Avg. Saturated Moisture content 52 Shrinkage ratio 0.13 (%) Maximum dry unit weight, Optimum moisture Content (%) 27 14.52 kN/m3

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4. Soil Sampling and Moreland Clay Characterization The Moreland Clay samples were obtained from a local test pit in Bossier City, Louisiana in accordance with ASTM D1452-09 (ASTM 2009) for disturbed soil samples and ASTM D1587/D1587M-15 (ASTM 2015) for undisturbed soil samples. Soil sampling site was chosen using the “websoil survey” website to make sure it is the Moreland clay even before soil sampling had been performed. The samples were retrieved in sealed containers and transported to the Geotechnical Testing Laboratory at the Louisiana Tech University. A series of laboratory tests were performed on the retrieved soil samples. These regular soil tests and expansive soil exclusive tests helped understand the swell-shrink properties of the Moreland clay. Table 1 shows the comprehensive soil properties of the Moreland clay from various laboratory tests. Different researchers provided simple tables to identify expansive soils. Comparing the obtained plasticity index (PI = 51), activity (Ac = 1.3) and expansion index (EI = 101) with results in the tables provided by Peck et al. (1974), Skempton (1953) and Uniform Building Code (UBC 1997), respectively, it can be concluded that the Moreland clay is very expensive. 5. Experiment Design of the Soil Stabilization Once the Moreland clay characterization was completed, a stabilization method with CFAG would be designed. One easy way to measure soil stabilization is to perform consolidation tests following ASTM D2435-96 (ASTM 2010). With a series of consolidation tests subjected to different consolidation pressures completed, the void ratio vs. consolidation pressure curve in its logarithmic scale was plotted. Slope of the rebound curve, the swelling index Cs was a good indicator for the soil stabilization. As the soil was getting stabilized using CFAG or cement, the rebound curve would be more and more flat. LADOTD (2016) recommend using 9% lime with 6% cement to stabilize expansive soil with the PI value in between 26-35, which is far less than the Moreland clay’s (PI = 51). In this experiment 10% cement was used to form a baseline performance and it was compared with the 5%, 10% and 20% CFAG stabilized soil, respectively. All the percentage described previously are percent by weight. Each batch consisted of three samples. Generally, CFAG is used with its caustic activators, which may cause safety issues. For this reason, water-added geopolymer was developed in construction industry, and it performs similarly to ordinary portland cement (OPC). In this research, to produce water-added geopolymer, METSO® 2048 from PQ® Corporation was used. The procedure of water-added CFAG is described as follows: 1) 60 gm METSO® beads were mixed with 100 gm water to make a solution as shown in Figure 5a; 2) 100 gm fly ash was taken and 3) Finally, 100 gm fly ash was then mixed up with 13 gm METSO® solution, creating 0.13 CFAG, which can be seen in Figure 5b. More detail about METSO® solution can be found in the manufacturer website (PQ Corporation 2017). Once the CFAG was produced it was mixed with soil samples. The procedure for soil sample preparation is described as follows: 1. Samples of 500 gm expansive soil passed through 0.420 mm-sieve were mixed with 5%, 10%, 20% CFAG, or 10% cement by weight, respectively. 2. To have a thorough blend, additional water had to be added. To find the minimum amount of water to be added, water was added little by little to find the minimum moisture content

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needed to make a thorough homogeneous paste of soil and CFAG. In every batch, the same moisture content was maintained so that the final results could be comparable with each other. The moisture content was found to be 27%, and different amount of water was added with 5% CFAG, 10% CFAG, 20% CFAG and 10% cement soil mixtures to make sure every batch had a 27% moisture content. Once the soil batches were produced, they were placed in tube-like containers. In the containers soils were placed in three layers with 30 tamping for each layer. After being tamped the samples were covered with a plastic cover to get air dried as shown in Figure 6. The curing was taken as a 7-day, 14-day and 30-day period, respectively. After curing, the soil samples were taken out of the containers and again placed in the consolidation ring in three layers with 30 tamping for each layer. Consolidation tests were performed on the twelve samples, as illustrated in Figure 7.

(a) (b) Figure 5 (a) METSO® Solution and (b) 0.13 CFAG

Figure 6. Stabilized Soil Samples in the Curing Process

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Figure 7. Consolidation Tests of the Stabilized Soil Samples 6. Consolidation Test Results of the Stabilized Soil Samples Figures 8 to 10 show the results of the consolidation tests of all the twelve soil samples. Finally, the relations between the compression index (Cc) and the swelling index (Cs) with curing time are shown in Figures 11 and 12. Table 2 shows the performances of the CFAG- and cementstabilized Moreland clay samples. The performance was measured using both of the compression and swelling indices. Especially, if the swelling index becomes smaller, the heave or shrinkage of the treated Moreland clay will be smaller after its moisture content varies. It is seen from Table two that, on the average, the swelling index of the stabilized soil with 10% CFAG is 2.5 times greater, and that with 20% CFAG is 2 times greater than the swelling index of the 10% cement stabilized soil. 1.35 1.25 1.15

Void ratio, e


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0.85 0.75 10

100 Pressure, P (kPa) Figure 8. The Seven-Day Soil Stabilization

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100 Pressure, P (kPa) Figure 9. The Fourteen-Day Soil Stabilization

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100 Pressure, P (kPa) Figure 10. The Thirty-Day Soil Stabilization Cc for 5% CFAG Cc for 20% CFAG

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Cc for 10% CFAG Cc for 10% Cement

0.40 0.35 0.30 0.25 0.20 0.15 0

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20 25 30 35 Days Figure 11. Relations between the Compression Index and Curing Time

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Cs for 5% CFAG Cs for 10% CFAG Cs for 20% CFAG Cs for 10% Cement

Swell Index, Cs

0.08 0.06 0.04 0.02 0.00 0

20 25 30 35 Days Figure 12. Relations between the Swelling Index and Curing Time

Swelling Compression Index Index


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Table 2. A Summary of the Soil Stabilization Lab Tests % Increases in the Indices Actual Lab Test Results as Compared to OPC 5% 10% 10% CFAG 20% CFAG 10% CFAG 20% CFAG CFAG OPC 0.4152 0.3986 0.3820 0.2325 71 64 0.3986 0.3820 0.3707 0.1827 109 103 0.3654 0.3488 0.2990 0.1827 91 64 N/A 90 77 0.0997 0.0830 0.0664 0.0332 150 100 0.0664 0.0498 0.0332 0.0166 200 100 0.0498 0.0332 0.0332 0.0166 100 100 N/A 150 100

7. Conclusion Based on the experimental results, it is concluded that the Moreland clay is highly expansive by nature and CFAG is an acceptable material for stabilization of the Moreland clay. The stabilization effect on expansive soils from different stabilizers were measured by using the swelling index, which is a good indicator for swelling or shrinkage degree after the moisture content of the stabilized Moreland clay varies. The study shows that cement is by far a better stabilizer for the Moreland clay as compared with geopolymer material in terms of the values of the swelling indices shown in figures 8 through 12 and table 2. However, when using CFAG to stabilize the Moreland clay, the stabilization effect can be improved by increasing the percentage of CFAG. Hopefully this research will help LADOTD or DOTs of other states to consider seriously CFAG as an alternative to replace cement and/or lime to stabilize expansive soils. The research achievements will provide valuable information for LADOTD in the future to enhance the standard specifications of roads and bridges in using fly ash as a soil stabilizer. Future research includes performing X-ray Fluorescence (XRF), X-ray diffraction (XRD) and

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crystallographic analysis of stabilized soil to better understand the properties of CFAG and its clay stabilizing mechanism. A thorough investigation on cost-benefit analysis in between cement and CFAG is also needed before the results are implementable in engineering practice.


8. Acknowledgement The research presented in this paper was sponsored by the South Plains Transportation Center (SPTC) under contract SPTC14.1-76. The authors would like to express their gratitude to Dr. William B. Patterson, Dr. Mohammad Readul Islam, Dr. Carlos Montes, Dr. Md Rashedul Islam and Shams Arafat at Louisiana Tech University for their comments that greatly improved the manuscript. References Abu-Farsakh, Y, M., and Chen, Q. (2012). "Evaluation of the Base/Subgrade Soil under Repeated Loading: Phase II–In-Box and Alf Cyclic Plate Load Tests." Louisiana Transportation Research Center, Baton Rouge, LA, 1-97. Abu-Farsakh, M., and Nazzal, M. (2009). "Evaluation of the Base/Subgrade Soil under Repeated Loading: Phase 1–Laboratory Testing and Numerical Modeling of Geogrid Reinforced Bases in Flexible Pavement." Louisiana Transportation Research Center, Baton Rouge, LA, 1-139. AHTD (2014). "Composition." Cement Treated Base Course, Arkansas State Highway and Transportation Department, Little Rock, Arkansas. Al-Homoud, A. S., Basma, A. A., Husein Malkawi, A. I., and Al Bashabsheh, M. A. (1995). "Cyclic Swelling Behavior of Clays." Journal of Geotechnical Engineering, 121(7), 562565. Al-Malack, M. H., Abdullah, G. M., Al-Amoudi, O. S. B., and Bukhari, A. A. (2016). "Stabilization of Indigenous Saudi Arabian Soils using Fuel Oil Flyash." Journal of King Saud University - Engineering Sciences, 28(2), 165-173. ASTM (2009). "Standard Test Methods for Soil Exploration and Sampling by Auger Borings." Annual book of ASTM standards, ASTM, West Conshohocken, PA. ASTM (2010). "Standard Test Methods for One-Dimensional Consolidation Properties of Soils Using Incremental Loading." Annual book of ASTM standards, ASTM, West Conshohocken, PA. ASTM (2015). "Standard Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes." Annual book of ASTM standards, ASTM, West Conshohocken, PA. Buhler, R. L., and Cerato, A. B. (2007). "Stabilization of Oklahoma Expansive Soils using Lime and Class C Fly Ash." Proc., Problematic Soils and Rocks and In Situ Characterization, ASCE, 1-10. Chen, F. H. (1975). Foundations on Expansive Soils, Elsevier Scientific Pub. Co., Amsterdam, Netherlands. Çokça, E. (2001). "Use of Class C Fly Ashes for the Stabilizationof an Expansive Soil." Journal of Geotechnical and Geoenvironmental Engineering, 127(7), 568-573. Correia, A. A. S., and Rasteiro, M. G. (2016). "Nanotechnology Applied to Chemical Soil Stabilization." Procedia Engineering, 143, 1252-1259.

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Dang, L. C., Fatahi, B., and Khabbaz, H. (2016). "Behaviour of Expansive Soils Stabilized with Hydrated Lime and Bagasse Fibres." Procedia Engineering, 143, 658-665. Davidovits, J. (1991). "Geopolymers." Journal of Thermal Analysis, 37(8), 1633-1656. Davidovits, J. (1993). "Carbon-dioxide green-house Warming: What Future for Portland Cement." Symposium on Cement and Concretes in the Global Environment, Portland Cement Association, Chicago, 21. Dhakal, S. K. (2009). "Stabilization of Very Weak Subgrade Soil with Cementitious Stabilizers." M.Sc. Thesis, Louisiana State University, Baton Rouge. Du, Y.-J., Jiang, N.-J., Liu, S.-Y., Horpibulsuk, S., and Arulrajah, A. (2016). "Field Evaluation of Soft Highway Subgrade Soil Stabilized with Calcium Carbide Residue." Soils and Foundations, 56(2), 301-314. Duxson, P., Fernández-Jiménez, A., Provis, J. L., Lukey, G. C., Palomo, A., and van Deventer, J. S. J. (2007). "Geopolymer Technology: The Current State of The Art." Journal of Materials Science, 42(9), 2917-2933. Erzin, Y., and Erol, O. (2007). "Swell Pressure Prediction by Suction Methods." Engineering Geology, 92(3), 133-145. Etim, R. K., Eberemu, A. O., and Osinubi, K. J. (2017). "Stabilization of Black Cotton Soil with Lime and Iron Ore Tailings Admixture." Transportation Geotechnics, 10, 85-95. Fredlund, D. G., Rahardjo, H., and Fredlund, M. D. (2012). Unsaturated Soil Mechanics in Engineering Practice, John Wiley & Sons. Groenevelt, P. H., and Grant, C. D. (2004). "A New Model for the Soil‐water Retention Curve that Solves the Problem of Residual Water Contents." European Journal of Soil Science, 55(3), 479-485. INDOT (2008). "Criteria for Chemical Selection." Design Procedures for Soil Modification or Stabilization, Indiana Department of Transportation, Indiana. Islam, M. R. (2013). "Creation and Analysis of a Fly Ash Database for Facilitating the Standardization of Geopolymer Concrete " M.Sc. Thesis, Louisiana Tech University, Ruston, Louisiana. Jaditager, M., and Sivakugan, N. (2017). "Infnfluence of Fly Ash–Based Geopolymer Binder on the Sedimentation Behavior of Dredged Mud." Journal of Waterway, Port, Coastal, and Ocean Engineering, 143(5). Jahandari, S., Saberian, M., Zivari, F., Li, J., Ghasemi, M., and Vali, R. (2017). "Experimental Study of the Effects of Curing Time on Geotechnical Properties of Stabilized Clay with Lime and Geogrid." International Journal of Geotechnical Engineering, 1-12. Jones, D. E., and Holtz, W. G. (1973). "Expansive Soils-The Hidden Disaster." Civil Engineering, American Society of Civil Engineers, 87-89. Khan, M. A. (2017). "Influence of Moisture Content Distribution in Soil on Pavement and Geothermal Energy." Ph.D. Dissertation, Louisiana Tech University, Ruston, Louisiana. Khan, M. A., and Wang, J. X. (2017). "Application of Euler-Bernoulli Beam on Winkler Foundation for Highway Pavement on Expansive Soils." Proc., PanAm-UNSAT 2017: Second Pan-American Conference on Unsaturated Soils ASCE. (Accepted). Khan, M. A., Wang, J. X., and Patterson, W. B. (2017a). "A Study of the Swell-shrink Behavior of Expansive Moreland Clay." International Journal of Geotechnical Engineering, 1-13. Khan, M. A., Wang, J. X., and Patterson, W. B. (2017b). "Swelling–shrinkage Properties of Expansive Moreland Clay." Proc., PanAm-UNSAT 2017: Second Pan-American Conference on Unsaturated Soils ASCE. (Accepted).

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