CE 199 – Undergraduate Research Project in Civil Engineering Final Presentation of Research17 October 2012 Construction Engineering and Management Group Development of a Method for the Design and Performance Testing of Controlled Low-Strength Materials Containing Processed Class F Fly Ash KAZ MIKHAIL DAVID S. MAURILLO Undergraduate Student, B.S. Civil Engineering Program Institute of Civil Engineering, University of the Philippines Diliman E-mail:
[email protected] Advisers: Dr. Nathaniel B. Diola Professor, Director, Building Research Service, National Engineering Center, University of the Philippines Diliman Abstract: The main purpose of the study is to create a design method in mixing Controlled Low-Strength Materials (CLSM) using locally manufactured Class F fly ash by mixing actiual CLSM and testing for fresh (flowability and setting time) and hardened properties (unconfined compressive strength). Controlled Low-Strength Material is also commonly known as flowable fill or controlled-density fill. CLSM is a very versatile material made up of soil or fine aggregate, water, fly ash, and minimal cement. It is usually applied for pipe-bedding and filling, trench fills, backfills for retaining walls, slope stabilization, void fillings (e.g. walls, cracks, crevices), filling of abandoned spaces like underground tunnels and mines, and can also be used to support footings or shallow foundations. The main design target for CLSM is to ensure the mixes made are flowable, self-leveling, easy to pump in place, will not settle, will not exert uplift pressures due to swelling, and will be excavatable at later ages. Mix proportions leading to inexcavatable specimens will noted, and will provide further information in improving the mix design methodology. The study aims to determine the optimum proportions of material components of CLSM, namely cement, Class F fly ash, fine aggregate (sand), and water to ensure proper density, flowability, satisfactory setting time, and ease of pumping, and excavatability in the long run. Mixes of increasing fly ash from the threshold content that satisfies flowability to the maximum allowed by ACI 229 are mixed, and tested for the main properties of flow (slump), density, setting time, and unconfined compressive strength. Specimen samples used were ASTM C109 50-mm cubes, as allowed by ACI 229R-99. New adjusted mix proportions designed for excavatability are then made and tested for performance based on interpolations from the satisfactory trial mixes. From the actual results obtained, a comprehensive guide and methodology for mix design of CLSM were made that would be of use to future designers. A general design methodology, guide and recommendations for CLSM mixtures were also made based on the application of CLSM and the kind/type of materials that are utilized in the mix. 1. INTRODUCTION 1.1 Background and Problem Statement Controlled Low-Strength Material (CLSM), commonly known as flowable fill, is a hybrid material sharing both properties of concrete/mortar and well-compacted soils. CLSM typically consists of minimal cement, fly ash or other pozzolans, fine aggregates, and water. CLSM is a cheap, economical, durable, and alternative construction material that has properties of both concrete/mortar and compacted soil, and can be classified as somewhere in between the latter two. CLSM is primarily used as backfill material, for structural fills, void fills, pipe bedding and fills, and slope stabilization of embankments. CLSM is an effective alternative material when insitu compacted fill proves to be unsatisfactory (e.g. too weak bearing pressure) and has undesirable properties (settlement, swelling, etc.). The ACI Committee Report on Controlled LowStrength Materials (ACI 229R-99) defines CLSM as a self-compacted, cementitious material used primarily as backfill material substituting compacted soil. It is also defined as a resultant material having compressive strengths of 8.3 MPa (1200) or less [1]. The actual design and use of CLSM has been first reported in 1964; first used by the United States Bureau of Reclamation as pipeline bedding material 1 for the Canadian River Aqueduct Project, running 515 km from Amarillo to Lubbock, Texas [3]. The project cost was estimated to be 40% less than using standard conventional backfilling. CLSM is divided into two categories based on its long-term unconfined compressive strength. CLSM can either be classified as excavatable or inexcavatable. Standard practice classifies excavatable CLSM as having strengths between 0.3 – 0.7 MPa (50 – 100 psi), easily removable using hand tools. Performance specifications impose a 1.4 MPa (200 psi) maximum strength [2] for excavatable mixtures while mixtures with strengths up to a maximum of 2.1 MPa (300 psi) are still considered excavatble with the use of mechanical equipment (backhoes, etc.). The main advantage of CLSM as a substitute material for compacted fill is due to its desirable properties. CLSM is self-leveling, thus does not need compaction unlike in-situ soil. CLSM is flowable, making it pumpable, readily flowing and filling hardto-reach spaces compacted soil cannot. When in its hardened state, CLSM also does not settle; preventing the cracking or shearing of structures it carries (e.g. pavement bases). Most importantly, when CLSM is no longer needed, it can easily be removed, in the case of excavatable mix proportions. Also, CLSM utilizes as little cement as possible, and recommends 1. For convenience purposes the fly ash is referred to as PFA in the study. While CLSM is a versatile material most especially effective for highway construction works. 2 . In the United States. While there are several guidelines for mix proportioning and actual placement of CLSM already available [1. namely: flowability. in this case Class F fly ash. All the constituent materials utilized in the experiment mix proportions were satisfactory in accordance with the American Society for Testing of Materials Standards and other organizational standards. 4]. and unconfined compressive strength. Determine which mix proportions result in ‘lowstrength’ (excavatable) and ‘high-strength’ (inexcavatable) CLSM mixtures by actual design of CLSM and testing for the three priority properties. Being a relatively new material compared to concrete (which has been used since ancient times). The ACI Committee Report on Controlled Low-Strength materials (ACI 229R-99) states that there is still no unified code on the design of CLSM. namely: flowability. and other design properties for CLSM. CLSM also provides an economical and convenient alternative whenever conventional methods and materials prove to be unsatisfactory. The study focuses on the investigation of three main properties of CLSM.the use of fly ash as both pozzolan and enhancer of workability. reliable methodology in the design and quality control of CLSM mixtures. such as the incorporation of admixtures that retard the strength development of CLSM mixtures. this type of CLSM is more difficult to design. The first part of the methodology involves the investigation of constituent material properties utilized for CLSM. objective methodology for design and quality control specified for CLSM utilizing processed Class F fly ash. 6. 2. There are still no established guides and methods developed to consistently achieve the desired mix proportions of satisfactory performance properties in terms of flowability. setting time. reducing the time incurred by repetitive trial-and-error procedures. Determine effective means of suppressing the strength development of CLSM to ensure future excavatability of actual mixtures. setting time. verifying the reliability and applicability of the existing guides reviewed and incorporate and improve the guides to create a simple. LITERATURE REVIEW 2. compliant with ASTM C618 standards. 4. each state has their own set of guidelines on the mixing and placement of CLSM. Based on the results of the experimental program. setting time. setting time. The study is limited to a single type of fly ash. Develop mix proportions that guarantee excavatability. which is much cheaper than using cement alone. The study also is limited to the approach of designing excavatable CLSM without chemical intervention. with the focus on utilizing processed Class F fly ash into CLSM mixtures: 1. organized design and performance directive for CLSM regardless of materials utilized to reduce the time. 2. CLSM is a relatively new material. Optimize the mix proportions of CLSM by investigating the factors affecting flowability. nor do they give detailed instructions and cautions to the designers of CLSM. when future removal is of concern. the design of CLSM is not yet defined and well-established. 2. reportedly been first used in 1964 by the US Bureau of Reclamation for pipe bedding. and unconfined compressive strength. unconfined compressive strength.1 Constituent Materials Of importance in this study is the investigation of the effects of performance properties of CLSM due to the amounts of PFA incorporated into the mixtures. and unconfined compressive strength. 1. its main drawback lies on its design. effort and resources expended by disorganized trial-and-error schemes in designing CLSM. The variability of the constituent materials as well their properties also makes designing CLSM difficult to generalize. The main content of the methodology being developed contains the following. density. Trial-and-error in mix proportioning is performed until the appropriate mix proportions based on the intended construction application are achieved [1]. locally produced Class F fly ash. it is important to be able to come up with an accurate. 3. marketed as ‘Maximizer’ and manufactured and distributed by Pozzolanic Philippines Inc.3 Scope of Work The research aims to assess the feasibility and practicality of actual CLSM designs utilizing Class F fly ash and other locally available constituent materials. While CLSM mixtures within the excavatable category find a wide range of applications. The main disadvantage of CLSM over compacted soil is that CLSM gains strength over time.2 Objectives With the urgency to use CLSM due to its versatility. they are very general and do not specify specific cases. Develop a general. unlike soil due to the presence of cement and other pozzolans. It can also determine the amount of water that can be added beyond the requirement to improve flow without segregation. PFA generally acts as a cementitious substitute due to the impracticality of only using cement in CLSM. Drinking water is usually very suitable for mixing CLSM. and older anthracite and bituminous coals. is a coal-combustion by-product. reducing time and costs in placement. 2. Shorter setting times indicate shorter waiting time before CLSM can carry design loads (e. and free of any impurities.3 Fine Aggregates Fine aggregates generally contribute to the strength. footings.g. in terms of suppressing the strength development of CLSM. ASTM C403 [1] ASTM D6023 [1] ASTM D4832. ASTM C109. and excavatability of CLSM.2 Class F fly ash Class F fly ash. such that pavement bases or other works to be supported by CLSM must be placed as early as possible. The initial setting time of CLSM as defined by the test is the first time duration in hours when the Vicat needle penetration is less than 25 mm. pipes etc). 2. The test determines the water demand of a particular amount of PFA in CLSM required to achieve satisfactory flowability represented by a slump or flow diameter of 200 mm (8 inches) or higher. segregation control. referred to as PFA in this study. permeability. traffic loads. almost pure. 2. ACI 229R-99 as well as other documents [2] provides comprehensive information on the control properties of CLSM.2 Setting Time When time constraints in construction need to be addressed. Water used in CLSM must be non-toxic. and effectively links with the binder to form more cohesive CLSM to avoid excessive segregation. The hydration reaction of cement in water produces calcium hydroxide that reacts with PFA to form cementitious compounds. ASTM C39 [1] ASTM D1883 [1] 3 .2.1. Flowability of flow consistency is measured using ASTM D6103: Test Method for Flow Consistency of Controlled Low Strength Material [1]. Blended hydraulic cements conforming to ASTM C595 can also be used. It is produced from burning of harder. Three of these properties are given special interest and investigated in this study.1. Type I and II Portland cements generally compliant with ASTM C150. CLSM is of a thick liquid-like consistency in its fresh state. PFA also improves the workability and flow properties of CLSM. Table 2: List of control properties of CLSM Property Flowability Setting Time Density Unconfined Compressive Strength Bearing capacity 2. Setting time for this study is measured by a modified Vicat penetration test (ASTM C191). Setting time generally takes 3-5 hours after placement of CLSM. the setting time of CLSM is of utmost importance. adapted for CLSM mixtures. ACI 229 primarily recommends the use of fine aggregates passing ASTM C33 specifications. ASTM D6024. Its other purpose is to serve as an activator of pozzolans in PFA that contribute to the strength and cohesion of CLSM.4 Water Water that is acceptable for mixing concrete is acceptable for mixing CLSM as well. giving it its flowability. coarse aggregates are excluded in CLSM due to difficulty in suppressing strength in CLSM.3] ASTM C33 [1] 2. empirically measured as the time when in-place CLSM can support the weight of a person. AASHTO M 157 [1.1.1 Cement Cement generally acts as binder for CLSM aggregates. Standard ASTM C150 [1] ASTM C618 [1] ASTM C94. providing the basis for strength and cohesion. The section discusses the priority properties investigated in the study.1 Flowability Flowability gives the advantage of CLSM to be pumped and fill hard-to-reach spaces. Generally.2.The following table shows the standards conformed by the actual materials in the study used to create trial mix proportions of CLSM. ASTM C94 and AASHTO M 157 provides specifications for water used in CLSM mixes.1.2 Properties of CLSM There are many properties of CLSM that are advantageous compared to conventional backfill materials. The table below summarizes basic CLSM properties and their standard methods for investigation and quality control. Fine aggregates fill voids in CLSM. Control Standard/s ASTM D6103 [1] ASTM C191. 2. Table 1: List of material standards for CLSM Constituent Material Cement Fly Ash (Class F) Water Fine Aggregates 2. The first batch aims to determine the effect of the amount of PFA in CLSM on the compressive strength development of the mixtures.3 – 1. Table 3: Categorization of unconfined compressive strengths of CLSM mixtures Category Excavatable Strength (Range) 0. 4 .3 MPa Uses Pipe bedding.2 Flowability Flowability studies were performed to determine the relationship between fly ash volume in CLSM and its corresponding water demand to achieve good flowability (200 mm or 8 inch slump according to ASTM D6103). 3. Table 4. al. while inexcavatable mixtures are designed when CLSM is utilized as a base course for pavements and structural fills. Excavatability is guaranteed by very ‘low-strength’ CLSM mixtures when intended for general purpose backfilling and pipe beddings. Cement contents of 1-3% by weight per unit volume of CLSM provides high chances of excavatability by keeping the strengths low due to cementitious cohesion. it also tests the applicability and reliability of following existing design guides in actual mixing of CLSM using the materials specified within the study. roadside trench fills.1 MPa max) 2. general purpose backfills Highway base course. structural fills 3. al. as included by ACI 229R-99 in the list of allowable test specimens. et. Sample specimens used were ASTM C109 50-mm (2 in) cubes particularly used for mortar specimens. void fill.1 – 8. EXPERIMENTAL PROGRAM Trial mixtures with the materials selected for CLSM mix proportions are subject to tests in order to obtain information on the factors that affect the properties of CLSM the study aims to investigate.2. Material quantities were expressed in kg/m3 of CLSM (Weight of components per 1 cubic meter of CLSM).1 Mix Proportioning Mix proportions involved two batches. Secondly. It is thus crucial to optimize the amount of cement used in order to ensure excavatability of CLSM. Strength increases as the cement content increases. [4] suggest that cement content typically determines the unconfined compressive strength of CLSM. [4]). The following table shows the observed water requirement to achieve a flow diameter of 200 mm and above (8 inches) based on ASTM D6103 flow cylinder tests performed. Table 4. The second batch of mix proportions makes an attempt on designing excavatable CLSM based on first-hand information obtained from the first mix proportioning scheme. Fresh properties of flow consistency and setting time was first investigated before sampling specimens subjected to unconfined compressive strength tests. et. Hardjito.3 Unconfined Compressive Strength The projected construction application of CLSM is determined by the unconfined compressive strength.2 Mix Proportions II of the experiment 3. in order to give an estimate on the possible amounts of PFA that would guarantee excavatability.2. Hardjito.0 MPa (2. Figure 1: relationship of strength development of CLSM with amount of cement in the mixtures (D.1 Mix Proportions I of the experiment Inexcavatable Studies on CLSM that D. 3.Table 5: Water requirement to achieve good flow consistency. on the premise that relatively weak CLSM still has enough allowance for strength development and will still be excavatable at later ages. The goal of this section is to verify whether the actual setting times determined agrees with the 3-5 hours range of satisfactory setting time for CLSM [1].92 300 200 100 0 0 200 114. Mix Proportions I The first trial mix proportions involve the determination of the suitable PFA amounts guaranteeing excavatability and to determine a trend of strength development with respect to the amount of fly ash used in CLSM.3 Setting time The setting time range for the actual mix proportions were determined using the Vicat needle test previously discussed. or retardation of the strength of CLSM is necessary to ensure due to CLSM gaining strength over by the presence of cementitious Figure 3: Compressive strengths.4 MPa (200 psi). 7. Mix Proportions I Mean compressive strengths. To determine potentially excavatable mix proportions in as early as 28 days (especially due to timeconstrained projects). The following figures show the strength development of the mix proportions during the first and second batches to determine amounts of fly ash leading to inexcavatability. Table 6: Setting times for trial mix proportions Figure 2: Strength development of CLSM as amount of fly ash increases in the mixture.75 400 600 800 1000 1200 1400 mean f'c psi Class F fly ash content. kg/m3 3.4 Unconfined Compressive Strength Suppression development excavatability time caused compounds. psi 500 400 460 307.92 182. Mix Proportions II 5 . Mix Proportions I Compressive Strength. Figure 4: Strength development.54 43. ACI as well as other organizations [2. 8] set the 28-day strength maximum limit as low as 1.67 132. RESULTS AND DISCUSSION Based on the experiments and analysis performed. 5.8333 35.5417 35 0 5 4 5 -5 -5 -5 14 14 5.375 43.1667 34. In the setting time experiment.2083 200 150 50 22. the water demand to achieve good flow consistency decreases. 7.5 14 14 14 0.4.75 66. 4. The more saturated CLSM is. as PFA increases in the mixture.5 35. However. Increasing the water content for a particular fly ash volume beyond the water demand for flowability increases the flow diameter further. For relatively high amounts of PFA (300-400 kg/m3). CONCLUSION By using the approach of designing CLSM that is excavatable. Segregation was not a serious problem with the highly saturated mixtures as PFA as well as the fine aggregates were not hygroscopic and easily drained out excess water out of the mixtures. leading to disintegration when immersed in water after 24 hours (parallel study performed). Mixtures with low water-to-binder ratios. Increasing the amount of Class F fly ash in CLSM definitely decreases the water demand for satisfactory flowability.7917 38. leading to inexcavatable mixtures. . 2. Note that inexcavatability increases with the amount of fly ash in the mixtures. due to the decreased water demand.7547 31. It is important that discretion must be observed in adding water so as not to result in lack of component cohesion and segregated mixtures. and in worst cases.375 33. 600 Compressive Strength. based on what CLSM will be used for.1 75500 002 550 5075 7525 250 2 7 3 3 2 3 3 2 3 3 3 3 a a a a a a a a a a a a pf pf pf pf pf pf pf pf pf pf pf pf Figure 7: Early strength development retardation of CLSM mix proportions (2nd batch) by increasing water-binder ratio. psi 300 250 200 150 100 77. In ensuring excavatability by adding water beyond the requirement. Only the amount of water established a relationship with setting time.625 44. the following conclusions were made: 1.75 114. Increasing w/b effectively retards strength gains.917 182. 5 and 14-day strength 300 Compressive strength. psi Boxplots. the amount of fly ash did not have an effect on the setting time of concrete. and retards the strength development of the mixture. Mix Proportions I PFA-CLSM 500 400 307.5 42. segregation and disintegration due to lack of cohesiveness between CLSM solid particles. adding water beyond the requirement causes saturation. The following tables show the developed methodology for designing CLSM that utilizes Class F fly ash to improve the 6 Figure 5: Low water-to-binder ratio (w/b) with increasing fly ash increases the strength of CLSM. PFA-CLSM Mixtures II.917 200 100 0 a pf 7 522 a pf 7 040 18 522 18 036 18 040 8 8 8 8 -1 -2 -2 -2 00 00 00 00 2 6 8 2 1 1 a a a a pf pf pf pf 35 a pf a pf a pf Figure 6: Batch I compressive strengths.542 132.1667 55. Adding the water content effectively retarded the strength gains of CLSM in order to achieve excavatable mixtures. exhibited by bleeding. 3. fresh properties are being compromised. The data collected enabled the development of a simplified mix design procedure for CLSM. the more time it requires to drain out excess water.667 460 300 282. pose the risk of inexcavatability due to higher strength developments. compromises were made when a relatively high amount of Class F fly ash is present. 3. leading to inexcavatable mixtures 6.25 31. implying threshold water requirement. setting the water content to the minimum required for good flowability did not retard the strength development. In the flowability experiment.05 300 200 87. South Carolina State Department of Transportation (SC-M210. Du. add water.001 cubic meters of volume (1 L). Trejo. This method can be further expanded and improved into a local design book for CLSM specifications in a Philippine setting. 7 .1.0 1. al. Kansas City. water demand is attained.4 > 1. 5.1.4 > 2. 7. Add 100 mL of water. American Concrete Institute.0 . 7. Table 8: 1st phase.200 Excavatable > 200 Inexcavatable > 300 Inexcavatable REFERENCES Table 10: Recommended mix proportions 1. 6. Hardjito. Foliard. determination of the type of CLSM for the project Table 13: Decision table for evaluation of setting time Table 9: Materials selection table Table 14: Unconfined compressive strength requirements 28-day strength (MPa) 0. 3. Concrete promotional Group. 06/07) 2. place into mixing bowl. C. measure slump. Tanijaya Sustainable development using Controlled-Low Strength Material. Adjust mix proportions to fill 0.1 Sampling Specimens of CLSM for Compressive Strength Specimen Description 50-mm cube ASTM C109 mortar cube specimens 75 x 150 mm cylinder ASTM D4832 CLSM plastic cylinder specimens 150 x 300 mm cylinder ASTM C39 concrete cylinder specimens CBR cylinder ASTM D1883 California bearing ratio specimens Table 12: Procedure for determining minimum good flow consistency Table 4: ASTM D6103 Summary to determine water demand of CLSM Equipment: mortar mixer. 1999 Guideline for Flowable Fill or CLSM-Controlled Low Strength Material. Du Development of a Recommended Practice for use of Controlled Low Strength Material in Highway Construction. Table 7: Step-by-step procedure for CLSM design Table 11: Allowable sample specimens for testing hardened CLSM Table 3.W. Folliard. and remix. et. 3. United States Guide Specification for Controlled Low Strength Material. ACI 229R-99. turn mixer on for 3 minutes. K. tape measure 1. American Concrete Institute Committee Revised Committee Report on Controlled Low-Strength Materials.workability and complement the minimum amount of cement in the mixtures. D. Chuan. J. 75 x 115 mm cylinder. Trejo. D.1 Table 6: Strength Requirements 28-day strength (psi) Category 30 . 2. L. 2008 Supplemental Technical Specification for Flowable Fill. Pour contents into cylinder and raise immediately. Select mix proportions (excluding water).150 Very Excavatable 150 . Add water in increments of 10 mL until a slump of 200 mm occurs.2 . 5. If slump diameter is less than 200 mm. National Cooperative Highway Research Program (NCHRP Report 597). 4. If slump diameter is 200 mm (8 inches). 4. National Ready-Mixed Concrete Association Controlled Low Strength Materials (CLSM) Utilizing Fly Ash and Bottom Ash. 6.