Clegg Hammer Research Articles

Short communication: Use of the Clegg hammer measure as an indicator of stall-surface compressibility in tie-stall housing and its relationship with stall comfort

Stall base and stall surface (i.e., with or without bedding) are key risk factors in cow comfort in dairy herds. In Canada, rubber mats, concrete floors, and mattresses are the most common stall bases used in tie-stall systems. Straw, wood shavings, and sand, at variable depths, are the most commonly used type of bedding. The Clegg hammer (Clegg Impact Soil Tester Hammer; Lafayette Instrument Company, Lafayette, IN) is a tool used by engineers to test the compressibility of pavement or golf course surfaces. Recently, this tool has also been used to measure the compressibility of the stall surface on freestall dairy farms. A total of 32 tie-stall dairy herds were selected in Québec to test the usefulness of the Clegg hammer as a tool to assess stall surface compressibility in tie-stall housing. This study had 2 main objectives: (1) identify the location and the number of measurements needed to obtain a stable indicator of compressibility, and (2) identify differences in the compressibility of the stall surface depending on the stall base and bedding depth. On each farm, we tested the compressibility of 10 stalls. No significant differences were found between the front and the back of the stall for the location of the Clegg hammer measures. The differences in readings of the Clegg hammer were nonsignificant after the third measure taken at the same location, meaning that 3 measures are sufficient at one location to obtain a compressibility measure. Significant differences were found among the different stall base and surface combinations tested. Rubber mats were less compressible than mattresses. When a large quantity of bedding (>7.5 cm) was added on top of rubber mats, the compressibility results were equal to those of mattresses ≥10 yr old without bedding. To appropriately test the compressibility of stall surface in tie-stall farms, we recommend measuring the compressibility of the stall base on its own and with the usual amount of bedding used on the farm. Our study establishes that both stall base and surface affect compressibility, and that a large quantity of bedding helps increase the compressibility of the bed, especially on a harder stall base.

Production of sediment from the running surface of unpaved legacy roads in southeast Ohio, USA

ABSTRACTUnpaved, or unbound aggregate, roads are thought to be one of the largest anthropogenic sources of fine sediments in the stream channels of small watersheds. Sedimentation can reduce water quality in streams negatively impacting aquatic habitat as well as being a detriment to municipal drinking water sources. Even during periods of low-volume use roads can be a chronic source of fine sediment. Legacy roads may degrade stream water quality more than newly built roads as they were constructed before modern best management practices. This study measured the production of sediment from the road surface of a legacy road system within a small watershed using controlled precipitation experiments to determine the mass of sediment that roads could produce during one storm event. Sediment production was not related to road slope or strength as measured by Clegg hammer. The production of sediment from the road surface increased 95% on average with wet traffic use. Using an estimated road and stream connectivity of 50%, surface runoff from the roads in Middle Creek watershed could account for 16% of the total sediment yield from the watershed during a small summer storm event. Compacted tire tracks were utilized as flow paths during runoff experiments, emphasizing the importance of continual maintenance and best management practices. This study highlights the need to disconnect unbound aggregate roads from stream channels in order to prevent negative water quality impacts associated with sedimentation.

Estimating the resilient modulus of crushed recycled pavement materials containing crumb rubber using the Clegg impact value

Since the determination of resilient modulus (Mr) from the repeated load triaxial test is rather complicated, due to the expensive procedure and time-consuming nature, attempts have been made to estimate it using other properties, such as the unconfined compressive strength and California bearing capacity based on empirical models. However, because of the dynamic nature of the Mr, it should be estimated by other simple-procedure dynamic properties. The Clegg hammer test has been considered as an alternative since it is not only dynamic in nature but also simple and quick. There has been no report of any previous study on correlating between CIV and Mr of construction and demolition (C&D) aggregates containing crumb rubber. In this research, a series of experiments were conducted to measure the Mr and CIV of the waste crushed rock (WCR) and recycled crushed concrete (RCC) mixed with the rubber of two different sizes and different contents (0, 0.5, 1, and 2%) for making a green pavement. The experimental results show that the CIV and Mr of both aggregates increased with the fine crumb rubber components but decreased with the coarse rubber content. The increase of CIV and Mr due to the increase of fine rubber percentage can be attributed to the filler effect of fine rubber particles that provides better interfacial bonding condition. The analytical results show that a strong correlation exists between the Mr, confining stress, deviator stress and the CIV with the R2 value ranging from 0.74 to 0.99.

Geogrid for unsealed forest roads: installation considerations and bearing capacity testing in New Zealand

ABSTRACTThis study established 10 field trials on corporate forest roads in New Zealand to demonstrate geogrid installation procedures and test for differences in bearing capacity, hereafter referred to as road strength, for road segments with and without geogrid reinforcement. The primary objective of this research was to determine if thinner aggregate surface layers could be used in conjunction with geogrid reinforcement without significant reductions in road strength. Each trial consisted of three 25-m long road segments randomly configured with the following pavement designs: (1) Control section that consisted of a single aggregate layer overlying a compacted subgrade soil; (2) Geogrid reinforcement that used the same aggregate thickness as the Control; and (3) Geogrid + Reduced Aggregate treatment that used a thinner aggregate layer. Road strength was measured with a Clegg Hammer for the prepared subgrade, finished road surface (i.e. before traffic), and after one winter of log truck traffic. Overall, there were no clear differences in road strength among treatments before or after trafficking. Several factors related to studying operational forest roads are thought to have contributed to this finding, including relatively low traffic volumes (285–1220 loaded trucks) and variability in aggregate thickness within and among sites. Geogrid-reinforced roads may perform better over time and with more traffic. In terms of cost, this finding supports the common practice of simply using thicker aggregate layers to achieve a desired strength as long as aggregate is cheap, local, and readily available.

Recycled concrete aggregate/municipal glass blends as a low-carbon resource material for footpaths

Construction and Demolition (C&D) materials comprising recycled concrete aggregate (RCA), fine recycled glass (FRG) and a blend comprising 85% RCA with 15% FRG (85RCA/15FRG) were evaluated for their viability as footpath base layers. The geotechnical laboratory evaluation assessed the performance of the C&D materials in footpath bases and included particle size distribution, particle density, water absorption, pH, organic content, modified Proctor compaction, Los Angeles Abrasion and California bearing ratio (CBR) tests. Total concentrations and Australian standard leaching procedure tests were performed on several heavy metals to assess the leaching potentials of contaminants released from the recycled materials. Following the completion of the geotechnical and environmental laboratory evaluation, a footpath was constructed to demonstrate the performance of the 85RCA/15FRG blend as a footpath base material. Field tests comprising nuclear gauges for density and moisture measurements and Clegg hammer tests for field CBR measurements were undertaken to assess the performance of the base materials in the field. The 85RCA/15FRG blend was found to be an optimum one in the laboratory and field evaluation works, as the blend provided adequate bearing strength and furthermore enhanced the workability of RCA, through the introduction of glass fines. Energy savings assessment demonstrated that the use of 85RCA/15FRG blend as footpath base material furthermore has the potential for saving embodied energy. This research indicates that this low carbon concept, utilizing RCA and FRG blends as base materials, is a viable alternative engineering material for future footpaths.

One, two, three or four: Does the number of Clegg hammer drops alter ground hardness readings on natural grass?

The Clegg hammer is currently used to measure hardness of natural turf surfaces to inform performance and safety decisions. However, the number of Clegg hammer drops reported in natural grass testing varies from one to four drops, and the impact of the choice of the number of drops is unknown. The aim of this article is to determine whether significant differences exist between the four Clegg hammer drops on natural grass across a variety of conditions. Hardness readings (using a 2.25 kg Clegg hammer), soil moisture and botanical composition were recorded at nine different sites on seven football fields during an 18-week playing season. A total of 1255 hardness readings were collected for each of four consecutive Clegg hammer drops. Overall, there were significant differences between drop 1 and the other three consecutive drops, on all fields and on all sites. Deep soil moisture was the only factor that significantly influenced the hardness readings. The results of this study demonstrate that the decision regarding the number of drops recorded needs careful consideration as conclusions drawn on playability of a ground or the association with injury risk may vary considerably depending on the number of drops.

Validation of a Laboratory Method for Evaluating Dynamic Properties of Reconstructed Equine Racetrack Surfaces

BackgroundRacetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior.ObjectiveTo develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties.MethodsTrack-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression.ResultsMost dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces.ConclusionsLaboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD).Potential RelevanceDynamic impact properties of race surfaces can be evaluated in a laboratory setting, allowing for further study of factors affecting surface behavior under controlled conditions.

Ground hardness and injury in community level Australian football

ObjectivesTo describe the risk and details of injuries associated with ground hardness in community level Australian football (AF). DesignProspective injury surveillance with periodic objective ground hardness measurement. Methods112 ground hardness assessments were undertaken using a Clegg hammer at nine locations across 20 grounds, over the 2007 and 2008 AF seasons. Details of 352 injuries sustained by community level players on those grounds were prospectively collected as part of a large randomised controlled trial. The ground location of the injury was matched to the nearest corresponding ground hardness Clegg hammer readings, in gravities (g), which were classified from unacceptably low (<30g) to unacceptably high hardness (>120g). ResultsClegg hammer readings ranged from 25 to 301g. Clegg hammer hardness categories from low/normal to high/normal were associated with the majority of injuries, with only 3.7% (13 injuries) on unacceptably high hardness and 0.3% (1 injury) on the unacceptably low hardness locations. Relative to the preferred range of hardness, the risk of sustaining an injury on low/normal hardness locations was 1.31 (95%CI: 1.06–1.62) times higher and 1.82 (95%CI: 1.17–2.85) times higher on locations with unacceptably high hardness. The more severe injuries occurred with low/normal ground hardness. ConclusionsDespite the low number of injuries, the risk of sustaining an injury on low/normal and unacceptably hard grounds was significantly greater than on the preferred range of hardness. Notably, the severity of the injuries sustained on unacceptably hard grounds was lower than for other categories of hardness.

Injury risk associated with ground hardness in junior cricket

ObjectivesTo establish if there is an association between ground hardness and injury risk in junior cricket. DesignNested case-series of players who played matches on specific grounds with objective ground hardness measures, within a prospective cohort study of junior community club cricket players. MethodsMonitoring of injuries and playing exposure occurred during 434 matches over the 2007/2008 playing season. Objective assessment of the hardness of 38 grounds was undertaken using a Clegg hammer at 13 sites on 19 different junior cricket grounds on the match eve across the season. Hardness readings were classified from unacceptably low (<30g) to unacceptably high (>120g) and two independent raters assessed the likelihood of each injury being related to ground hardness. Injuries sustained on tested grounds were related to the ground hardness measures. ResultsOverall, 31 match injuries were reported; 6.5% were rated as likely to be related to ground hardness, 16.1% as possibly related and 74.2% as unlikely to be related and 3.2% unknown. The two injuries likely to be related to ground hardness were sustained whilst diving to catch a ball resulting, in a graze/laceration from contact with hard ground. Overall, 31/38 (82%) ground assessments were rated as having ‘unacceptably high’ hardness and all others as ‘high/normal’ hardness. Only one injury occurred on an objectively tested ground. ConclusionsIt remains unclear if ground hardness is a contributing factor to the most common injury mechanism of being struck by the ball, and needs to be confirmed in future larger-scale studies.

Reliability of equipment for measuring the ground hardness and traction

The aim of this paper is to report the inter-rater reliabilities and intra-rater reliabilities of the Clegg hammer, penetrometer, and studded-boot apparatus used for measuring the mechanical properties of natural turf, and to determine whether the level of experience influences the reliability. Three experienced and three novice testers measured the surface hardness and rotational traction at nine locations on a community-level Australian football oval. A repeated-measures analysis of variance tested for significant differences between the six testers for all equipment, and intra-class correlation coefficients (ICCs) were calculated to determine the inter-rater reliabilities and intra-rater reliabilities. The ICCs for the reliability between the six testers ranged between 0.77 and 0.87 for the Clegg hammer, ranged between 0.55 and 0.73 for the penetrometer, and equalled 0.51 for the studded-boot apparatus. The inter-rater reliabilities and intra-rater reliabilities were greater for the experienced testers than for the novice testers for the Clegg hammer and penetrometer but the novice testers produced greater inter-rater reliabilities for the studded-boot apparatus. This study highlights the potential variability that can exist between testers using the ground hardness and traction equipment, which has implications for future research involving multiple testers both in agronomic-based studies and in linking the surface properties to the injury risk across multiple venues.

Biomechanical Response to Changes in Natural Turf During Running and Turning

Integrated biomechanical and engineering assessments were used to determine how humans responded to variations in turf during running and turning. Ground reaction force (AMTI, 960 Hz) and kinematic data (Vicon Peak Motus, 120 Hz) were collected from eight participants during running (3.83 m/s) and turning (10 trials per condition) on three natural turf surfaces in the laboratory. Surface hardness (Clegg hammer) and shear strength (cruciform shear vane) were measured before and after participant testing. Peak loading rate during running was significantly higher (p < .05) on the least hard surface (sandy; 101.48 BW/s ± 23.3) compared with clay (84.67 BW/s ± 22.9). There were no significant differences in running kinematics. Compared with the "medium" condition, fifth MTP impact velocities during turning were significantly (RM-ANOVA, p < .05) lower on clay (resultant: 2.30 m/s [± 0.68] compared with 2.64 m/s [± 0.70]), which was significantly (p < .05) harder "after" and had the greatest shear strength both "before" and "after" participant testing. This unique finding suggests that further study of foot impact velocities are important to increase understanding of overuse injury mechanisms.

Development of a Correlation Model between a 20-kg Clegg Hammer and Field CBR for Measuring Subgrade Strength in Forest Roads in Western Oregon

Much of the forest industry in the western United States does not require control of compaction on forest road subgrades despite the potential economic and environmental gains from improved subgrade construction. Development of tools such as the Clegg impact hammer allow for rapid testing of the subgrade during construction, and Clegg Impact Values (CIV) have been correlated with more robust soil test values such as the California Bearing Ratio (CBR) that are often used for road design. A new correlative model that relates the CBR to 20 kg CIV was developed entirely from field data, differing from previously developed models that used laboratory-prepared soils. Another advantage of this model is that it uses a 20-kg Clegg impact hammer. The 20-kg Clegg impact hammer has a larger testing area than the more common 4.5-kg Clegg impact hammer; thus, there is less influence from small deviations in the soil matrix due to items in the fill such as rocks or organic matter. The correlation coefficient for this model is 0.71, which is lower than that for models previously developed from laboratory results. The use of a lower bound, one-tailed, 90% confidence limit is presented as a useful design model to determine a conservative of soil strength that can be measured directly during construction.

Fine Aggregate Angularity from Geotechnical Perspective

ABSTRACT Particle angularity is an important aspect in the performance of asphalt concrete pavements. When rounded materials are used, the shear strength is reduced resulting in rutting and shoving of the asphalt concrete mixtures. Currently, the Superpave design method stipulates that the fine aggregate angularity (FAA) via AASHTO T304 be used as a test specification for fine aggregate. The objectives of this paper are to examine a number of methods for characterizing fine aggregate characteristics of aggregates commonly used in asphalt concrete pavements. Five different sands comprising of five different gradations utilizing a partial factorial experiment. The 19 different gradation and aggregate source combinations are tested using the Fine Aggregate Angularity Test Method C as outlined by AASHTO T304 (2003) and ASTM C1252 (2003), the direct shear test, compacted aggregate resistance (CAR) test, modified light Clegg Hammer, and an aggregate imaging system device. Statistical analysis of the test results are conducted to evaluate if the various tests can discriminate between the five different sources of materials and five different gradations. This paper will discuss particle angularity from a geotechnical point of view and it will hopefully answer the question: Do these tests really measure fine aggregate angularity and which test or tests should be used to measure the angularity of sands for use in asphalt concrete mixtures? The experimental testing results show that the CAR test and AIMS properties (i.e. gradient angularity, radius angularity, and 2D Form) are able to distinguish between different gradations and aggregate type (manufactured versus natural sands). The direct shear test and modified light Clegg Hammer test were able to distinguish between natural versus manufactured sands, however they were not able to distinguish among the variations in gradation. Therefore the CAR test and/or AIMS device are suitable candidate tests for determining the angularity of fine aggregates. These methods of characterizing fine aggregate, however, should be compared to the performance of asphalt concrete mixtures through laboratory and field performance.

Measurement of Granular Fill Compaction Using Low Frequency Vibration Testing

This paper describes the use of an instrumented impact hammer test for density measurement in a granular soil (Specification for Highway Works Type 1 fill) whilst monitoring the performance of vibro-tamper compaction. A 3–D finite element model was also used as a predictor. The effect of varying key material properties was studied. An increase in the soil's modulus of elasticity resulted in higher natural frequencies. An impact hammer, fitted with a force transducer, was used to excite the soil whose response was measured by accelerometer and analysed in both time and frequency domains. The change in natural frequencies of the modes of soil vibration was observed after each pass of a vibro-tamper. A sudden increase in natural frequencies was observed after the first pass; this effect reduced with compaction. Shear wave velocities were used to calculate a low strain modulus of elasticity and a correlation was established with the modulus of elasticity derived from Clegg hammer impact values. The same type of tests were applied to understand the field attenuation characteristics of Type 1 fill. There was a slight decrease in the maximum amplitude of the shear waves with increasing compaction; high attenuation of shear waves was also noted.

Field Testing of Stabilized Soil

Remediation of a Superfund site in Stratford, Connecticut, involved stabilization of the subgrade with portland cement. Part of the remediation site was to be used as a parking area. The stabilized soil was to be covered with natural base/subbase course materials and capped with an asphalt concrete cover. During the course of the remediation, a base-course layer could not be placed prior to the onset of winter. A field study was conducted to quantify any changes in the mechanical properties of the open stabilized subgrade subjected to freeze-thaw cycling during the winter of 1996-1997. Field evaluation was conducted with pavement industry tools: the Clegg impact hammer and the dynamic cone penetrometer. Evaluation results show the viability of the Clegg hammer as an instrument for quality assurance and also show that there can be up to 50% loss in compressive strength of the subgrade within the uppermost layer of the material caused by freeze-thaw cycling.

Field tests on pavement foundations

Abstract Generally the California Bearing Ratio (CBR) is used to quantify the properties of subgrades for use in pavement design. In the last few years, a wide variety of less familiar, but potentially more useful, tests has been developed. This paper describes some trials in which the results of Dynamic Cone Penetrometer, Clegg Hammer and Falling Weight Deflectometer tests are compared. Comparisons with the output of an instrumented vibrating roller and Plate Bearing Test results are also made. The practical problems of relating the collected information to the engineering properties (particularly stiffness) of the soil are discussed and some tentative proposals for dealing with these problems are put forward.