See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/312186080 A novel test to determine the workability of slipform concrete mixtures Article in Magazine of Concrete Research · January 2017 DOI: 10.1680/jmacr.16.00234 CITATIONS READS 0 190 3 authors: Xuhao Wang Peter Taylor Chang'an University Iowa State University 44 PUBLICATIONS 132 CITATIONS 88 PUBLICATIONS 225 CITATIONS SEE PROFILE Xin Wang Iowa State University 8 PUBLICATIONS 5 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Concrete Internal Curing View project Ice- and snow-free pavements View project All content following this page was uploaded by Xuhao Wang on 30 May 2017. The user has requested enhancement of the downloaded file. SEE PROFILE Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Magazine of Concrete Research, 2017, 69(6), 292–305 http://dx.doi.org/10.1680/jmacr.16.00234 Paper 1600234 Received 18/05/2016; revised 06/10/2016; accepted 19/10/2016 Published online ahead of print 09/01/2017 Keywords: fresh concrete/rheological/rheological properties/ vibration/workability ICE Publishing: All rights reserved A novel test to determine the workability of slipform concrete mixtures Xuhao Wang Xin Wang Project Manager, National Concrete Pavement Technology Center; Adjunct Assistant Professor, Iowa State University, Ames, IA, USA (corresponding author: wangxh@iastate.edu) Graduate Research Assistant, Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA, USA Peter Taylor Director, National Concrete Pavement Technology Center, Iowa State University, Ames, IA, USA The science of rheology is not strictly applicable for low workability of slipform concrete mixtures because such mixtures are not fluids. However, the workability of slipform concrete mixtures can be assessed using the concepts behind describing rheological behaviour. Understanding the workability of a mixture is important for construction activities to achieve a successful pavement. Too dry a mixture may cause problems achieving sufficient consolidation, while too wet a mixture may result in edge slump. The novel workability test method (vibrating Kelly ball test or VKelly test) presented in this paper quantitatively assesses the responsiveness of a dry concrete mixture to vibration, as desired of a slipform paving mixture. The development process was carried out in three phases to achieve costeffectiveness, portability, ability to assess critical performance parameters and repeatability. The three phases were assessing the sensitivity of the VKelly test to check whether it can signal variations between laboratory mixtures with a range of materials and proportions, evaluating the test in field applications at a number of construction sites and validating the test against the box test developed at Oklahoma State University. The VKelly test appears to be suitable for assessing a mixture’s response to vibration (workability) with a low multiple operator variability. A unique parameter, the VKelly index, is introduced, and a mixture in the range of 2·0–3·0 cm/s1/2 seems to be suitable for slipform paving. Introduction It has always been a challenge for the concrete industry to define and predict the workability of concrete mixtures. While concrete can easily meet the specifications with respect to hardened properties, describing the workability of a concrete mixture can be very elusive (Cook et al., 2013). The aggregate system, paste quality and paste quantity can all influence the workability, but modelling these effects is largely empirical (Koehler and Fowler, 2003). Moreover, there are unique requirements for slipform paving concrete mixtures – they should be stiff enough to avoid edge slump yet flow readily under vibration. The science of rheology may be applied to concrete but, being the study of fluids, may not be strictly applicable to low-slump concrete. However, the concept of a two-parameter measurement may still be considered useful to properly describe a mixture. The method developed and assessed in this work considers the rate of movement under vibration as well as the yield stress to characterise a mixture. The objective of this work was to develop a workability test method that can quantitatively assess the responsiveness to vibration of dry concrete mixtures, as is desired of a mixture suitable for slipform paving. The proposed test method aims at achieving cost-effectiveness, portability, the ability to assess critical performance parameters and repeatability. The work to 292 refine and evaluate the method was carried out in the following three phases. (a) Assess the sensitivity of the VKelly test to check whether it can signal variations between laboratory mixtures with a range of materials and proportions. (b) Evaluate the VKelly test in field applications at a number of construction sites. (c) Validate the VKelly test against the box test developed at Oklahoma State University. Background Workability test methods The term ‘workability’ has been defined in several ways by different authorities. & & The Japanese Association of Concrete Engineers defines workability as ‘that property of freshly mixed concrete or mortar that determines the ease and homogeneity with which it can be mixed, placed, and compacted due to its consistency, the homogeneity with which it can be made into concrete, and the degree with which it can resist separation of materials’. Mindess et al. (2003) define it as ‘the amount of mechanical work, or energy, required to produce full compaction of the concrete without segregation’. Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution & The American Concrete Institute (ACI, 2008) states that workability is ‘that property of freshly mixed concrete or mortar that determines the ease with which it can be mixed, placed, consolidated, and finished to a homogenous condition’. Test methods to measure the workability and rheological performance of fresh concrete, from no-flow to self-consolidating concrete, have been developed since the early twentieth century. The most widely used method for ordinary concrete mixtures is the slump test developed by Abrams (1922). Before the adoption of supplementary cementitious materials and water-reducing admixtures, the slump test could not only measure the consistency of freshly made concrete but also, to some extent, could indicate the potential performance of a hardened concrete mixture due to the fact that it is (normally dramatically affected by) water content. However, the increasing complexity of mixtures has meant that this correlation is no longer valid. From a rheological point of view, if a concrete material is considered to be a Bingham fluid, two scientific parameters – yield stress and plastic viscosity – can be applied to characterise its rheological behaviour. Thixotropy, a time-dependent shear thinning parameter, can also be determined under dynamic conditions. According to Koehler and Fowler (2003), most existing workability test methods can be split into either single-point or multi-point tests depending on how many parameters they can actually measure. The slump test, for instance, is categorised as a single-point test because of its ability to measure yield stress only. The National Institute of Standards and Technology (NIST) classifies workability test methods into four categories (Hackley and Ferraris, 2001) & & & & confined flow tests – the material flows under its own weight or under an applied pressure through a narrow orifice free flow tests – the material either flows under its own weight, without any confinement, or an object penetrates the material by gravitational settling vibration tests – the material flows under the influence of applied vibration; the vibration is applied by using a vibrating table, dropping the base supporting the material, using an external vibrator, or using an internal vibrator rotational rheometers – the material is sheared between two parallel surfaces, one or both of which are rotating. Koehler and Fowler (2003) summarised the available workability test methods into different categorises and the advantages, disadvantages and performance criteria of these test methods are listed in Table 1. VKelly test method development Kelly ball test The Kelly ball test was developed in the 1950s in the USA and formerly standardised in ASTM C360-92: Standard test method for ball penetration in freshly mixed hydraulic cement concrete (Bartos et al., 2002; Ferraris, 1999). Due to lack of use, it was discontinued by ASTM in 1999, but continued to be applied by the California Department of Transportation in Test 533 (CDoT, 2014). It can be conducted as a field test for measuring the consistency of plastic concrete. It is comparable to the slump test, yet is considered to be more accurate and reliable (Scanlon, 1994). However, the precision of the test declines with the increasing size of coarse aggregate (Bartos, 1992). The major disadvantages and drawbacks of using the Kelly ball are summarised in Table 1. The Kelly ball test apparatus consists of a 15·2 cm steel cylinder with a hemispherically shaped bottom (as shown in Figure 1). The shaft is graduated in 0·64 cm increments and slides through a frame, and this acts as a reference for measuring the depth of penetration. The total weight of the apparatus (ball, shaft and handle), exclusive of the yoke, is 13·6 ± 0·05 kg. The ball is placed on a level concrete surface and the depth of penetration is recorded after the ball is released. The slump is typically about twice the Kelly ball test reading for normal-weight concrete (Koehler and Fowler, 2003). From a rheology point of view, the Kelly ball test provides an indication of the yield stress of the sample because the stress applied by the weight is equal to the yield stress of the concrete for the area under the ball. However, this may not be able to provide useful information for very low slump concrete or highly thixotropic concrete because the applied stress is not sufficient to overcome the yield stress of concrete (Ferraris, 1999). Overview of the proposed VKelly test method The VKelly test apparatus (Figure 2) is built on the Kelly ball apparatus with a vibrator attached to the ball. After several trials, the vibrator was modified by drilling out the eccentric weight in order to control the amount of energy delivered to the sample. Five 0·95 cm diameter holes were drilled from the weight, as shown in Figure 3. As such, it delivers 58% of the original 0·0087 N.m. The steel ball was trimmed to maintain the original apparatus weight of 13·6 kg so that it is still functional as a static Kelly ball. The Iowa Department of Transportation specifies that vibration should be in the range of 5000 to 8000 vibrations per minute (vpm) in order to deliver sufficient energy while limiting the risk of compromising the air-void system by beating too much air out of the mixture (Tymkowicz and Steffes, 293 294 Parameters measured Workability by graduated scale, K and W terms K-slump tester (Nasser probe) Yield stress Viscosity and yield stress Slump test Modified slump test Free flow test methods Time of concrete flow out of tube Orimet test (free orifice test) Confined flow test methods Compaction Compactability, factor test non-linear relationship to slump Test Stable Stable Commercially available, good Stable Good, commercially available Ruggedness Similar to slump test 1·5–23·0 cm Medium- and highworkability concretes High-slump concrete 0–18 cm Workability range Similar to slump test Up to 3·8 cm Greater than 1·0 cm cannot fit Up to 2·5 cm Larger apparatus up to 4 cm Aggregate size restrictions Similar to slump test Cheap Fair Cheap Expensive Cost Fast 1 min Fast Moderate Similar to slump test Simple Simple Simple Moderate Test speed Complexity Similar to Similar to slump test slump test Small Moderate Moderate Moderate Sample size Table 1. Summary of features of existing workability test methods (Taylor et al., 2015a) Similar to slump test Quick and direct result Direct reading on workability and compactability Quick and direct result Moderate Data processing One person One person One person Similar to Similar to slump test slump test Small and portable Portable Light Advantages Adds parameter of time to the slump test ASTM C143 (ASTM, 2012a); EN 12350-2 (CEN, 2000a) in Europe & Well known and widely used device worldwide & Specifications are typically written in terms of slump & Results can be converted to yield stress based on various analytical treatments and experimental study & Simple to perform and only requires slightly more equipment than the slump test & Gives an indication of both yield stress and plastic viscosity & Gives more information than the slump test & Dynamic test is more appropriate than static tests for highly thixotropic mixtures Needs modification & Inexpensive and for low-slump simple to use mixtures & Quick and provides a direct result & Good simulation of actual placing conditions & Sensitive to changes in fine aggregate content US Patent & Direct result, 3 863 494 simple and (Nasser, 1975) easier than slump test & Can be performed on in situ concrete & K and W terms provide more information than slump Number of people required Remarks Heavy (over More than Widely used in 36 kg) one Europe Size and weight Powers (1968) Wilby (1991) Bartos (1992) Bartos et al. (2002) References Ferraris (1999) Bartos et al. (2002) (continued on next page) & Static test, not a Ferraris and dynamic test; does de Larrard not account for the (1998) thixotropy of Ferraris (1999) concrete or the ability of concrete to flow under vibration & Need to verify the validity of the test ASTM C143 & Does not give an indication of viscosity (ASTM, & Static, not dynamic 2012a) EN 12350-2 test; results are influenced by (CEN, 2000a) concrete thixotropy & Less relevant for higher slump mixtures & Does not consider the effects of coarse aggregate & Static test; not appropriate for lowslump mixtures & Only appropriate for Bartos (1992) Bartos (1994) highly flowable and self-compacting Wong et al. concrete (2000) & Results are not expressed in terms of fundamental units & Large and bulky & Requires a balance to measure the mass of concrete & May not reflect the field situation & Does not use vibration Disadvantages Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Slump, slump flow, and slump time Penetration correlated to the slump Penetration correlated to yield stress Penetration, correlates to slump and Vebe time Time to flow a certain distance Torque measured from concrete mixing truck Slump rate machine Kelly ball test Ring penetration test Cone penetration test Flow through test Deliverychute torque meter Stable Stable Stable Need a level concrete surface Wide range Highly flowable concretes Low-slump and fibrereinforced mixtures Not specified Not specified Not specified Good for grouts Not for large and highaggregate workability concretes Little expensive Cheap Cheap Cheap Cheap Up to 3·8 cm Stable Similar to slump test Similar to slump test Complicated in Similar to slump Similar to field conditions test slump test Long duration Fast Fast Fast Concrete in Fast the truck 6l Small Small Small Similar to Similar to slump test slump test Simple Simple Simple Simple Simple Similar to slump test Quick and direct result Quick and direct result Quick and direct result Quick and direct result Quick and direct result Similar to slump test Portable 1 m long, 0·23 m wide 4 kg metal cone Portable One person One to two persons One person One person Little One heavier person than slump test Similar to Similar to slump test slump test US Patent 4 332 158 (Osborne, 1982) Not widely used Not a well-known test Not a well-known test Developed in the 1950s in the USA; alternative to the slump test A computercontrolled device Wong et al. (2000) Bartos et al. (2002) Sachan and Kameswara Rao (1998) Wong et al. (2000) Powers (1968) Bartos (1992) Scanlon (1994) Ferraris (1999) Chidiac et al. (2000) (continued on next page) & Static test, not a dynamic test; does not account for the thixotropy of concrete or the ability of concrete to flow under vibration & Requires computer to log data and calculate & Faster than the & Static test slump test and & Must be performed on a level concrete more accurate in determining surface consistency & The test is no longer widely used & Provides an & Large aggregate indication of can influence the yield stress results & Easy and simple & Static test, perform on a level concrete to perform surface & Can be performed on & Large aggregate can influence the in situ concrete results & Test is not widely used and the interpretation of results is not well known & Provides a direct & Static test, not result and easy particularly to perform appropriate for & Can be fibre-reinforced performed on in concrete situ concrete & Not recorded in fundamental units & Simple and & Only appropriate inexpensive for highly flowable concrete & Test results are a function of the & Not standardised and time required for not widely the concrete to used flow both out of the cone and down the trough & Measures the & Gives no indication of workability of plastic viscosity the concrete as it & Readings are made at exits the mixer only one shear rate before it is & Device needs placed calibrating for & Direct reading of each mixture torque from device & No need for computer or other sensors & Gives an indication of both yield stress and viscosity & A simplified traditional rheometer and less expensive Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution 295 296 Surface settlement versus initial concrete height Parameters measured Degree of compaction compactability Flow table test Thaulow tester Powers’ remoulding test Low- to moderateslump concrete Better for highslump concrete Workability range Not specified Not specified Aggregate size restrictions Inappropriate for Commonly used Up to 5 cm field use for low-slump mixtures Stable Stable Ruggedness Fair Expensive Cheap Little expensive Cost Similar to Vebe test Minimum 23 kg Small Small Sample size Fair Fair Fast Long until concrete hardens Simple Simple Simple Fair, uses LVDTs Test speed Complexity Horizontal spread of Stable, but a cone specimen needs to be subjected to jolting placed on firm level ground Wide range of concretes Not specified Fair As slump cone test, 0·007 m3 Fast Simple Similar to the Powers remoulding test, but modified to allow for the measurement of concretes with higher workability Similar to Vebe test, Inappropriate for Commonly used Not specified different apparatus field use for low-slump mixtures Vebe Remoulding ability consistometer of concrete under vibration Compaction test Vibration test methods Surface settlement test Test Table 1. Continued Direct results Direct results Direct results Quick and direct result Does not give a direct result Data processing One person Fair Heavy Heavy One person At least one At least one DIN 1048 and EN12350-5 (CEN, 2000b) ASTM C124 (withdrawn in 1973) ASTM C1170 (ASTM, 2008) EN12350-4 (CEN, 2004); similar to Fritsch test Can be used for moderate slump mixtures Number of people required Remarks 200 by 400 One mm rigid metal container Fair Size and weight Disadvantages Bartos et al. (2002) References & Only works for lowslump concretes & Size of the device generally unsuitable for field work & No analytical treatment of the test method has been developed & Shear rate declines during vibration & Size of the device generally unsuitable for field work & No analytical data available (continued on next page) Tattersall (1991) Wong et al. (2000) Bartos et al. (2002) ACI 211 (ACI, 2002) Powers (1968) Scanlon (1994) Wong et al. (2000) & Size of the device Bartos (1992) Scanlon (1994) generally unsuitable Bartos et al. for field & Only works for low(2002) slump concretes & No analytical treatment of the test method has been developed, shear rate declines during vibration & Difficult to empty for Bartos et al. low-slump concrete (2002) & Different compaction Ferraris (1999) methods cannot be compared directly & May need a computer to facilitate readings & Measures higher workability than that measured with the Vebe and the Powers remoulding tests & Simple and can & Does not represent be used in the actual placement field conditions & Direct result & Results tend to & Appropriate for converge as the highly thixotropic number of drops is concrete increased & An analytical treatment of the test is difficult & Provides an indication of compactability & Simple and inexpensive & Can give an indirect indication of plastic viscosity when the variable of time is added & Dynamic test; can be used on very dry concrete & Standardised in ASTM and identified by ACI 211 (ACI, 2002) in its guide for proportioning low-slump concrete & Test results are directly obtained & Dynamic test and suitable for low-slump concretes & Test results are directly obtained & Inexpensive and & Does not give a simple to direct result perform & Time required to & Appropriate for a perform the test is wide range of longer than other concrete test methods mixtures because settlement distance must be recorded until concrete hardens Advantages Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Fair Discharge rate of concrete falling from chute to bucket with vibration Similar to the LCL flow test, Angles flow box and the vibrating slope apparatus Vibratory flow meter Stable Low-slump concrete Low- to moderateslump concrete Vibrating slope apparatus Stable for lab use Penetration depth versus time Not specified Expensive Cannot be too Expensive large due to the apparatus Cheap Vertical pipe apparatus Up to 3·8 cm Specially for fibrereinforced concrete Stable Elapsed time from insertion of the vibrator until all concrete discharged Fair Inverted slump cone test Not specified Wide range of concretes Stable Wigmore Penetration consistometer resistance by adding energy Similar to Angles flow test; not suitable for very low or very high workability Not specified LCL flow test Inappropriate for Moderate field use slump mixtures Time of concrete to flow under vibration and pass obstructions Angles flow box test Large Fair As slump cone test, 0·007 m3 Fair Fair Fair Fair Fast Fast Fast Fair Fair, use displacement transducer Difficult to perform Simple Simple Direct results Direct results Direct Direct results Direct results Very heavy Fair Small and portable Large Fair ACI Committee 544 recommended — More than Developed in the two 1960s, modified people by Federal Highway Administration & Simple and direct results & Readily available equipment and materials & Dynamic test considering the high thixotropy of fibrereinforced concrete & Simple and direct results & Readily available apparatus & Dynamic and provides valuable information & By changing the vibration parameters, the test can be used to determine values related to yield stress and viscosity & Measures lowslump concrete & Results can be correlated to yield stress and viscosity & Designed to be rugged for field use & Dynamic test & Wide range of concrete workability Similar concept for & Represents SCC mixtures actual field conditions & Dynamic test that subjects concrete to vibration & The ability of concrete to pass obstructions and resist segregation is assessed & Similar to Angles flow box test More than Behaves as a one Newtonian fluid person subjected to vibration One person One person One person Szecsy (1997) Wong et al. (2000) Tattersall and Baker (1989) Banfill et al. (1999) Tattersall and Banfill (1983) ASTM (2001) Bartos et al. (2002) (continued on next page) & Very large, bulky and heavy device & Results have not been verified analytically & Needs a notebook computer to record data & Vibration is limited and shear rate is non-uniform & Not effective in distinguishing changes of mixtures & Different vibrators result in varied results & & & & & & & Scanlon (1994) Bartos (1992) & & & & More expensive Requires electricity Not precise Drop ball needs to be larger than the maximum coarse aggregate size Device is too large and bulky for field use Appropriate for mixtures with less than 5 cm slump Operation is tricky to maintain consistency Long fibres may wrap around the vibrator Important test parameters are not standardised Expensive and may not be suitable for field use Pipe has 60 mm opening may too small for normal aggregate sizes Scanlon (1994) Wong et al. (2000) & Not appropriate for field use & Results are likely a function of yield stress and viscosity, but the values are not directly recorded Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution 297 298 Visual rates, surface voids and edge slumping Parameters measured Dry unit weight and corresponding moisture content Intensive compaction test Density of compacted concrete Kango hammer Density of test compacted concrete Proctor test Methods for very low slump concrete Box test Test Table 1. Continued Stable Stable Stable Stable Ruggedness Not specified Not specified May up to 5·0 cm Aggregate size restrictions Slump less than Up to 3·0 cm about 1·0 cm Low-slump concretes Lean, dry concrete Slipform paving concrete Workability range Expensive Fair Cheap Cheap Cost Small cylindrical sample Cubic, small Small About 0·03 m3 Sample size 3–5 min Fair Simple Simple Very time Simple consuming Direct results Direct results Direct results Direct results Fast Simple Data processing Test speed Complexity One person One person About 54 kg One person & Can be used for low-slump mixtures & Simple and well known Designed for soil test & Equipment is expensive compared with the Proctor test; 150 mm model is too heavy for field use & Does not incorporate vibration, which is commonly used in placing low-slump concrete & Does not incorporate vibration and can be only used for lowslump concretes & Very time consuming, needs preparation & Hammer is not specified, making comparisons of test results difficult & Apparatus is large and requires electricity Juvas (1990) Tattersall (1991) Juvas (1994) Juvas (1994) Bartos et al. (2002) ASTM D698 (ASTM, 2012b) ASTM D1557 (ASTM, 2012c) & More work is needed Cook et al. to verify the rating (2013) scale & No field data available & No specifications for evaluating edge slumping & Simulates actual placement conditions & Simple and does not require expensive equipment & Suitable for slipform paving concrete & Repeatability is good for single and multioperators References Disadvantages Advantages & With vibration and pressure, the test accurately simulates field placement conditions & Simple and easy to perform Nordtest-Build 427 & Accurately (Nordtest-Build, measures small 1994), US patents changes in 4 794 799 proportions (Paakinen, 1989) & Simulates lowand 4 930 346 slump roller(Paakinen et al., compacted 1990) concretes & Fast and computer controlled & Smaller model feasible for field use Designed for soil test Developed at Oklahoma State University Number of people required Remarks Larger than One Proctor person test Small and portable Fair Size and weight Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Handle Graduated shaft 14·0 cm Steel frame 14·3 cm R = 7·6 cm 11·7 cm Steel ball Figure 2. VKelly test apparatus 300·0 cm All holes empty Figure 1. Kelly ball test apparatus 1996). A variable transformer is used to hold the vibrator frequency to 6000 vpm. The following procedures are recommended for the VKelly test on both static (CDoT, 2014) and dynamic tests (Taylor et al., 2015a). & & & & & Discharge fresh concrete into a wheelbarrow or other container to a depth of at least 15·0 cm for 2·5 cm aggregate or smaller, and at least 20·0 cm for concrete made with larger aggregate. Create a levelled area of about 0·3 m2 without tamping, vibrating or consolidating the concrete. Avoid overworking the surface, causing excess mortar to rise and resulting in erroneously high penetration readings. Gently lower the ball until it touches the surface of the concrete. Make sure the shaft is vertical (perpendicular to the surface of the concrete) and free to slide through the yoke. Take an initial reading to the nearest 0·2 cm and then gradually allow the ball to sink into the concrete. Record, to the nearest 0·2 cm, a second reading when the ball comes to rest. Turn on the vibrator, which has been pre-set to 6000–8000 vpm, and simultaneously start the timer. Record the readings on the graduate shaft at 6-s intervals up to 36 s. A video recorder can be used to help further analyse the penetration depth during vibration. Remove the VKelly apparatus, remix the test concrete for about 30 s and repeat the test twice. For any given time, Hole Figure 3. Modified eccentric weight in vibrator (Taylor et al. 2015a) & & 1: the penetrating depth should be within 1·3 cm of the average readings from the three measuring cycles. Plot the averaged penetration readings (vertical axis) against the square root of time (horizontal axis) (see Figure 4) and determine the slope of the best-fit line from √6 s to √36 s by conducting a linear regression analysis of the data (Equation 1). Report the slope, Vindex (in cm/s1/2) pffiffi Dpene ¼ Vindex t where Dpene is the penetration depth at time t, t is the elapsed time of vibration and Vindex is the VKelly index. Research significance The objective of developing a novel test protocol and defining a workability parameter is to provide a better approach for measuring slipform paving concrete consistency and assessing 299 Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Table 2. Chemical composition of cementitious materials Incremental penetration depth: cm 16·0 14·0 12·0 y = 2·1x R2 = 0·99 10·0 8·0 6·0 4·0 Sample of test results 2·0 Linear (sample of test results) 0 0 1 2 3 4 5 Vibration duration, 6 7 8 S½ Silicon dioxide (SiO2): % Aluminium oxide (Al2O3): % Iron oxide (Fe2O3): % Sulfur trioxide (SO3): % Calcium oxide (CaO): % Magnesium oxide (MgO): % Sodium oxide (Na2O): % Potassium oxide (K2O): % Phosphorus pentoxide (P2O5): % Titanium dioxide (TiO2): % Strontium oxide (SrO): % Barium oxide (BaO): % Loss on ignition: % Type I/II cement Class C fly ash 20·10 4·44 3·09 3·18 62·94 2·88 0·10 0·61 0·06 0·24 0·09 — 2·22 42·46 19·46 5·51 1·20 21·54 4·67 1·42 0·68 0·84 1·48 0·32 0·67 0·19 Figure 4. Sample plot of VKelly test results responses under vibration process. Such a mixture should be mobile while under vibration, making it easy to move the mixture through a paving machine and to achieve full consolidation while creating a slab with the required dimensions. On the other hand, the mixture should also be highly thixotropic, meaning that when vibration energy is no longer provided it will stand up straight without edge slump. The slump test only addresses the latter parameter. The approach was thus to take an existing test – the Kelly ball test – and modify it by adding vibration energy. water/cementitious materials (w/cm) ratio of 0·45, aiming at 5% air content. Class C fly ash was introduced as a supplementary cementitious material and a synthetic air-entraining admixture (AEA) was used. The chemical composition of the cementitious materials is shown in Table 2. The variables used were as follows. & & Experimental approach The development of the VKelly test method was conducted in three phases. & & & & & Phase I was to assess the sensitivity of the test to capturing variations in laboratory mixtures with a range of proportions and materials. A matrix was prepared and measured by (a) setting a control mixture, (b) incrementally adjusting a single ingredient, (c) conducting both slump and VKelly tests using more than one operator and (d) repeating for the other ingredients. Phase II was to run the VKelly test in the field to check its feasibility as a field test method at a number of slipform paving sites. Phase III sought to validate the VKelly test results by comparing it with the box test (Cook et al., 2014) carried out on the same mixtures. Phase I: Laboratory tests Materials and proportions The control mixture was an ordinary Portland cement mixture with 335 kg/m3 cementitious materials, a fine to coarse aggregate ratio of 45/55 (with local limestone aggregate (2·5 cm nominal maximum aggregate size) and river sand) and a 300 Sand: increments of 60, 120 and 240 kg/m3 and decrements of 60, 120 and 240 kg/m3 (respectively denoted as +1, +2, +4, −1, −2 and −4) Air: an increase of 2% and a decrease of 2%, yielding target air contents of 3% and 7% (respectively denoted as +2 and −2) Class C fly ash: increments of 10%, 20% and 30% Portland cement replacement dosage (respectively denoted as +1, +2 and +3) Water: increments of 5 and 10 kg/m3 (respectively denoted as +1 and +2). Including the repeated control mixture, a matrix of 22 mixtures was prepared. The mix proportions are shown in Table 3. Tests Samples of all the mixtures were subjected to testing for fresh properties, including slump (ASTM C143 (ASTM, 2015)), air content (ASTM C231 (ASTM, 2014b)) and unit weight (ASTM C138 (ASTM, 2014a)), and a VKelly test. Laboratory test results The test results are summarised in Table 4. A factor of two was used to convert the static initial readings to slump, which were nearly identical to the slumps measured in accordance with ASTM C143 (ASTM, 2015). The VKelly index as measured by two operators was assessed statistically to check multi-operator variation. The percentage Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Table 3. Mix proportions (Taylor et al. 2015a) Variable Sand Stone (CA): kg/m3 Sand (FA): kg/m3 Cement: kg/m3 Fly ash: kg/m3 Water: kg/m3 AEA: ml/cwt Air: % w/cm ratio Unit weight: kg/m3 FA/CA Air Class C fly ash Water Plain +1 +2 +4 −1 −2 −4 +2 −2 +1 +2 +3 +1 +2 1007 824 335 — 150 44 5 0·45 2316 0·45 947 883 335 — 150 44 5 0·45 2316 0·48 887 943 335 — 150 44 5 0·45 2314 0·52 765 1061 335 — 150 44 5 0·45 2311 0·58 1069 765 335 — 150 44 5 0·45 2319 0·42 1130 705 335 — 150 44 5 0·45 2320 0·38 1251 587 335 — 150 44 5 0·45 2322 0·32 979 800 335 — 150 44 7 0·45 2264 0·45 1036 848 335 — 150 44 3 0·45 2370 0·45 1007 824 301 33 150 44 5 0·45 2316 0·45 1003 820 268 66 150 44 5 0·45 2307 0·45 1000 818 234 100 150 44 5 0·45 2303 0·45 1007 824 335 — 155 44 5 0·46 2316 0·45 1007 824 335 — 160 44 5 0·48 2316 0·45 Table 4. Laboratory test results (Taylor et al. 2015a) Mixa Sand −4 Sand −2 Sand −1 Sand +1 Sand +2 Sand +4 Air +2 Air −2 Air −2 (R) Fly ash +1 Fly ash +2 Fly ash +3 Plain Plain(2) Plain(2) Water +1 Plain(2) Water + 2 Plain(3) Plain(4) Plain(3) 15 min Plain(3) 30 min Plain(3) 45 min Plain(4R) mix Plain(4R) 15 min Slump: cm Slump measured by VKelly test: cm 1·9 1·9 1·9 2·5 2·5 2·8 3·8 2·5 2·5 2·5 2·5 3·2 2·5 2·5 — — 3·2 3·2 — — — — — 2·0 2·5 2·5 2·5 4·4 3·0 5·1 3·3 2·5 3·8 2·8 3·8 3·2 2·8 3·2 4·1 2·8 2·3 3·4 2·7 2·3 2·5 2·7 VKelly index statistics Air content: % Unit weight: kg/m3 VKelly index (ave.) Operator 1 Operator 2 Difference Difference: % 4·8 5·3 4·5 5·5 5·4 4·5 7·0 3·5 5·8 5·0 5·0 5·5 4·5 4·7 — — 5·2 5·5 — — — — — 90·4 88·4 89·8 86·9 88·8 88·3 87·4 88·6 87·4 87·8 88·0 87·4 87·6 87·7 — — 88·2 87·8 — — — — — 1·19 1·18 1·18 1·45 1·26 1·85 1·67 1·55 1·63 1·60 1·72 1·82 1·48 1·54 1·79 1·87 1·58 1·71 1·55 1·56 1·38 1·71 1·70 1·14 1·17 1·14 1·47 1·27 1·83 1·68 1·55 1·60 1·63 1·73 1·80 1·47 1·54 1·83 1·88 1·55 1·70 1·53 1·54 1·40 1·68 1·66 1·24 1·19 1·22 1·43 1·24 1·88 1·67 1·55 1·65 1·57 1·71 1·84 1·50 1·55 1·75 1·85 1·61 1·73 1·57 1·57 1·37 1·74 1·75 −0·10 −0·03 −0·08 0·04 0·03 −0·05 0·01 0·00 −0·05 0·05 0·01 −0·04 −0·03 −0·02 0·08 0·03 −0·05 −0·03 −0·05 −0·03 0·03 −0·07 −0·09 8·31 2·15 6·45 2·63 2·02 2·74 0·30 0·00 3·13 3·17 0·74 2·09 2·06 0·99 4·40 1·36 3·38 1·48 3·11 1·80 1·83 3·86 5·37 a (2), (3), and (4) denote the second, third and fourth repeats; (R) denotes remix differences varied from 0·00 to 8·31% for the same test, which indicates a low multi-operator error. The repeatability of the VKelly test performed by a single operator was also verified. The plain mix was tested four times and the coefficient of variation of the index for the four mixtures was determined to be 0·06 cm/s1/2. The influence of elapsed time on the index was also tested, and the results are shown in Figure 5. Mix plain(3) was measured three times at 15-min intervals without remixing. The index tended to decrease with elapsed time, but the influence was not apparent until the measurement taken 45 min after mixing. The VKelly index was measured after remixing mix plain(4) right after the original measurement and after 15 min elapsed time. The remixing generally provided a stable index, as shown in Figure 5. The error bars shown in Figure 5 represent the standard deviation of all the plain tests (i.e. 0·09 cm/s1/2). 301 Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution 1·90 VKelly index: cm/s½ 1·80 1·70 1·60 1·50 1·40 1·30 1·20 1·10 s m Pl ix ai @ n( 4) 15 re m m in ix n( 4) ai Pl s 45 n( 3) ai Pl ai n( 4) re Pl Pl ai n( 3) 30 m in m m 15 n( 3) ai Pl in s s in n( 3) ai Pl n( 2) Pl ai Pl ai n 1·00 Figure 5. Influence of elapsed time and remixing on VKelly index Sand Air Fly ash Water 2·5 VKelly index: cm/s½ 2·0 1·5 1·0 Water Fly ash 0·5 Air Sand 0 –4 –3 –2 –1 0 +1 +2 +3 +4 Increment of variables Figure 6. Influence of fine aggregate, air, class C fly ash and water on VKelly index Figure 6 shows the effects of varying fine aggregate content, air content, class C fly ash content and water content on the VKelly index. An increase in fine aggregate content up to 240 kg/m3 increased the VKelly index, while decreases in content produced a lower index. Increases in class C fly ash dosage and water content within a reasonable range resulted in a gradually increased index value, as expected. However, the lower air content mixture had a higher index compared with that of the plain mixture. This is unexpected, and the reason for this is unknown. Phase II: Field tests VKelly tests were conducted at a number of slipform paving sites. Pavement types included reconstruction, bonded and 302 unbonded overlay, and new pavement, with pavement thicknesses varying from 10 cm to 30 cm. The mix proportions, site information and field test results are shown in Table 5 (Taylor et al., 2015a). VKelly slump values were in the range 2·5–6·6 cm. Site MO was found to have the lowest VKelly index, likely due to the low w/cm ratio and high daily average temperature. The low fly ash replacement level is likely related to the low index for site C, which is consistent with the laboratory test results discussed above. The modified aggregate system of sites F, G, H, I and J with either intermediate aggregate or coarse sand has the potential to affect the thixotropy and workability of the mixture, as indicated by the higher index at these sites. Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution 7/30/15 237 113 136 635 — 1179 — Gravel Yes Type A Interstate Unbonded overlay 22·9 6·6 2·0 22 6/1/15 237 101 128 814 — 705 290 Granite Yes Type A County Unbonded overlay 12·7 3·8 1·9 22 224 301 Limestone Yes WRDA 82 Highway New pavement 30·5 2·5 1·5 28 — Gravel Yes Type A Interstate Unbonded overlay 20·3 2·5 2·2 9 — Gravel Yes Type A Highway — Granite Yes Type A City Bonded overlay 10·2 2·5 2·0 18 Quartzite Yes Type A County Bonded overlay 12·7 3·8 2·1 26 — — Limestone Yes Type A Interstate Unbonded overlay 24·1 4·4 2·1 21 — Limestone Yes Type A City Reconstruction 22·9 5·7 1·8 23 7/22/14 325 81 154 739 — 980 In order to assess the limits of what mixtures may be considered ‘good’ or ‘bad’ for slipform paving, a validation process is necessary. Data were collected as part of another programme (Taylor et al., 2015b). Mixtures were prepared that ranged from deliberately dry to deliberately wet, so that the VKelly test could be performed over a wide range of workabilities. Two types of coarse aggregate were used, limestone and crushed gravel (LS and G), both of 2·5 cm nominal maximum aggregate size. Natural river sand was the same as that used in phase I. Two aggregate gradation systems were used for each aggregate type – one with a fixed 50/50 of coarse to fine aggregate content and one that was sieved to fit within a tarantula curve (Ley et al., 2012). A constant class C fly ash replacement level of 20% was used and the w/cm ratio was 0·42. Either two or three cementitious material contents were applied for each aggregate system. Tests were conducted to determine fresh concrete properties, including slump (ASTM C143 (ASTM, 2015)), air content (ASTM C231 (ASTM, 2014b)), the VKelly test and the box test (Cook et al., 2014). Figures 7(a) and 7(b) show the relationship between cementitious material content and slump and VKelly index, respectively. As expected, both parameters increase with increased cementitious material content. However, the VKelly index is more sensitive to the cementitious material content; that is, the VKelly test can differentiate between mixtures having similar slump values. Generally, the aggregate system that fell within the tarantula curve gave a better workability. The box test visual rating was assessed for each mixture and plotted against the VKelly index (Figure 8). A box test visual rate of 2·0 is considered to be acceptable for slipform paving (Cook et al., 2014), which corresponds to a VKelly index of 2·0 cm/s1/2. An index of 3·6 cm/s1/2 was measured in the 7·6 cm slump mixture, which is too wet for slipform paving. Therefore, a reasonable upper limit is considered to be 3·0 cm/s1/2. Conclusions 22·9 5·1 2·1 19 The following conclusions are drawn from this study. Thickness: cm VKelly slump: cm VKelly index Average temperature: °C Date (m/d/y) Cement: kg/m3 Fly ash: kg/m3 Water: kg/m3 Sand: kg/m3 Coarse sand: kg/m3 Coarse aggregate: kg/m3 Inter aggregate: kg/m3 Aggregate type AEA Water reducer Location Pavement type 7/17/14 237 101 135 745 — 1071 7/18/14 237 104 125 722 — 926 Limestone Yes Type A City Reconstruction 377 — — Gravel Yes Type A Highway Overlay using fabric 15·2 3·8 2·1 22 — 2·5 2·2 23 27·9 6·4 2·2 21 9/26/14 279 47 121 684 — 952 8/27/14 231 77 126 753 — 829 9/12/14 237 102 122 443 332 1071 8/29/14 237 101 125 645 240 959 8/15/14 237 95 113 698 — 811 8/14/14 237 101 125 758 — 1091 7/21/14 237 101 128 833 — 978 Site I Site MO Site H Site G Site F Site E Site D Site C Site B Site A Table 5. Mix proportions, site information and field test results Gravel Yes Type A Interstate Reconstruction Site K Site J Phase III: Validation of VKelly test results & & & The proposed VKelly test method appears to be suitable for assessing the response of a mixture to vibration (workability), especially for slipform paving mixtures. Two parameters from the VKelly test – slump and the VKelly index – can be used to report both static and dynamic characteristics of concrete mixtures. The VKelly test can be conducted in the field and may also find some uses as a quality control tool, although the 303 Magazine of Concrete Research Volume 69 Issue 6 A novel test to determine the workability of slipform concrete mixtures Wang, Taylor and Wang Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Slump: cm 20·0 18·0 16·0 14·0 12·0 10·0 8·0 6·0 4·0 2·0 0 200 report by the same authors (Taylor et al., 2015a). This research was conducted under the Federal Highway Administration (FHWA) Transportation Pooled Fund Study TPF-5(205) with support from the state departments of transportation of Colorado, Iowa (lead state), Kansas, Michigan, Missouri, New York, Oklahoma, Texas and Wisconsin. The authors would like to express their gratitude to Iowa Department of Transportation and the other pooled fund state partners for their financial support and technical assistance. G1.0 50 LS1.0 50 G1.0 tarantula LS1.0 tarantula 250 300 350 400 (a) REFERENCES 4·0 Abrams DA (1922) Proportioning concrete mixtures. ACI Journal G1.0 50 LS1.0 50 G1.0 tarantula LS1.0 tarantula VKelly index: cm/s½ 3·5 3·0 2·5 ASTM (2001) C995: Standard test method for time of flow of 1·5 1·0 0·5 0 200 250 300 350 400 Cementitious material content: kg/m3 (b) Figure 7. 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Your contribution will be forwarded to the author(s) for a reply and, if considered appropriate by the editorial board, it will be published as a discussion in a future issue of the journal. 305 View publication stats
