Sustainable Concrete Post Construction for Fencing and Trellising of Organic Crops

Project Overview

FNC07-684
Project Type: Farmer/Rancher
Funds awarded in 2007: $4,300.00
Projected End Date: 12/31/2009
Region: North Central
State: Ohio
Project Coordinator:
Stephen Pearce
Ohio River Vista Vineyard, Winery & Research Station

Annual Reports

Commodities

  • Fruits: grapes

Practices

  • Education and Training: demonstration, display, extension, farmer to farmer, mentoring, on-farm/ranch research, participatory research, workshop
  • Farm Business Management: new enterprise development, budgets/cost and returns, feasibility study, agricultural finance, value added
  • Sustainable Communities: new business opportunities, public participation, employment opportunities, social networks, sustainability measures

    Summary:

    PROJECT BACKGROUND
    The Ohio River Vista Vineyard and Research Station is located in Clermont County, Ohio. The 5.42 acre small family farm site overlooks the Ohio River as a southwesterly view 200 feet below and six-tenths of a mile distant. The unglaciated soil is rich in clay over limestone underlayment providing suitable drainage. To mitigate erosion, the vineyard rows are terraced east-west, perpendicular to the 30%, steeply-sloped ground. This ideal terroir is capable of supporting 3,000 vines producing as much as 1600 cases of fine wine per year. Vinifera varietals trellised include cabernet sauvignon and cabernet franc. French-American hybrid varietals include traminette and vidal blanc. A new field research facility (housing processing and laboratory test equipment along with experimental seedling cultivars) hosts faculty and students of nearby universities conducting collaborative projects.

    Since its inception in 2006, the farm has practiced sustainable organic grapevine growing and erosion control.
    PROJECT DESCRIPTION
    Project goals:
    • Find an optimal concrete substitute for treated wood posts to serve organic vineyards
    • Solicit feedback from experienced grape growers and other interested farmers
    • Construct a website to publish the project procedures and results

    Work Plan:
    • Design and fabricate various concrete posts for vineyard trellising and fencing
    • Determine the optimal post form factor based on suitability and cost
    • Subject the selected final configuration to testing for strength and durability

    RESULTS:
    • Cost-competitive concrete posts can be fabricated using a simple form (with or without pvc inserts)
    • Hi-tensile wire may be affixed to end posts with saddle clamps and simply placed (without fasteners) in pre-formed v-grooves of line posts, saving both labor and material
    • Extra-strength concrete post utilization allows spacing to be increased from the usual 12-18 feet to 30 feet, meaning fewer posts are required per acre of trellising
    • Concrete posts can be made and installed by one person capable of leveraging 134 pounds (i.e. lifting one end –about 67 pounds – at a time)
    • It is important to allow concrete curing for a minimum of 3 days (preferably 28 days for maximum hardening) before installing 2’ in the ground

    Concrete Post Design:
    A form was constructed using a 4’x8’ sheet of exterior plywood serving as a stiff (23/32” thick) base for 8-foot long 2”x4” studs affixed horizontally upright to make multiple compartments for the hardening of ready-mix cement. By this means, concrete posts were fabricated according to various designs with the intention of demonstrating that a sustainable trellis system could be built at a cost comparable to one utilizing conventional, non-sustainable wood posts.

    As a final design, line posts were formed with dimensions 3-1/2”x3-1/2”x 8’, and both corner and end posts with dimensions of 3-1/2”x4-1/4”x 8’. This meant that one bag of ready mix concrete was used for each line post and 1-1/2 bags were required to form end and corner posts. At one end of each post compartment a notch (or a hole in some configurations) in the form allowed positioning of a ½-inch rebar in the center along the length of each post. Ten foot lengths of rebar were used so that each post had 24-inches of steel protruding from the bottom of the concrete. The weight of line posts so constructed averaged 90 lbs, while the larger end posts averaged 130 lbs. in weight.

    Added to the basic post construction, v-grooves were formed along the sides by various means while the concrete began to set. (A commercial manufacturer of concrete posts would want to have this provision built into the form as an essential part of an automated process, perhaps with silicone spacers). For a single person operation it was found to be simple enough for slanted v-grooves to be added using a screwdriver pushed into the hardening cement at the appropriate levels along the sides to create voids. Another technique was to drill the grooves before the cement hardened.

    Because the project’s further focus was to produce a trellis system for grapevine support, and it was desired to meet the needs of all trellising systems including those of more complicated split canopies (such as the Geneva Double Curtain), additional features were added to the basic construction including perpendicular 1-inch holes cast into the top of the post to provide attachment points for transverse supports. These holes were formed using pvc tubing held in place by the wooden form. It was found that pvc-removal was best accomplished after a minimum of 3-days hardening to avoid cracking the concrete. Moreover, by applying a thin coating of silicone grease to the pvc before pouring the concrete, the pvc could be readily removed using a hammer to drive a second piece of same diameter pvc until the form could be readily disassembled.

    A smooth rounded top gave each post a more “professional” appearance. This was accomplished by adding to the top of the form a cut-in-half 3-1/2-inch length of 4-inch pvc tubing which readily detached after the concrete dried. An even more finished look was achieved by using a concrete edging tool to make smooth, curved sides on the face of each post. (If similar curved edges are desired on the other side of the post, the form compartments would have to include suitable curves).

    Another feature added to the face of end posts was the stenciling of the initials of the grapevine variety to be planted. It was found that suitable writing in concrete mix was impossible because of the large quantity of aggregate rock used as strengthener. To overcome this obstacle, cement mix (normally used for brick-or block-laying) was added to the surface where letters were to be impressed.

    A further embellishment distinguishes one block of grapevine variety from the next by having affixed a 4”x4” tile with a grapevine design. This likewise was more easily done by displacing concrete mix with some cement mortar mix to better bind the ceramic tile.

    Concrete Post Installation:
    Whereas an attempt was made to drive 28-day hardened concrete posts into heavy clay soil, it turned out that holes for post-setting had to be augured. Too many post tops were broken otherwise, perhaps because the entire force of the pile driver was applied to a single line at the curved top. A flat formed top may have helped, but the pile driver was rented for one day only and no flat-topped posts had been made.

    To install a post into an augured 2-foot deep hole, a 5-foot length of half inch rebar was first driven 2-foot into the center of the bottom of the hole, and then removed using a pipe wrench. Next, a 3-foot long two-inch aluminum angle was upright-positioned within the hole so that the vertex of one end of the angle rested at the half-inch hole opening while the upper part of the aluminum angle leaned against the side of the augured hole. It was then possible for one person to lift a post with the extending rebar in the groove of the angle. By further tilting the post upright the extending rebar followed the groove into the pre-punched hole, and the post rested upright without support. Next, clay was tamped into the hole surrounding the bottom two-foot of a line post. A spirit level was used to plumb the posts. End posts were at this point embedded in concrete after several failures occurred in tamped clay (even in one instance with the end post anchor installed). It was possible that 2,000 pound tensioning of the attached wires was tried too early after installing, but it was deemed safer to use a concrete base (at extra cost).

    Next, hi-tensile wire was attached to the end posts using two 5-cent saddle clamps (available on-line) per post. The vine support wires were then simply laid into corresponding v-grooves of each line post. Before tensioning, anchors were installed at each end post, first using buried concrete and rebar, but as time drew short, standard screw disc anchors were used. After first tensioning the anchor wires, the trellis wires were tensioned to 1 ton. It is important to note that whereas normal post spacing in vineyards does not exceed 18 feet, the extra strong concrete posts were successfully installed at 30 foot intervals. This further reduced the overall cost of the trellis.

    Finally, vines were affixed to the fruiting wires as per standard practice. As the growing season drew to a close, it was decided to wait for vine dormancy before fully load testing the trellis in order to avoid damaging vine shoots before winter hardening.

    Trellis Load Testing:
    After leaf fall, the trellis system was load-tested using thirty-six, 5-gallon buckets of water weighing fifty-six pounds each for a total load of about 1-ton. The considerable sag of the hi-tensile wire was re-tensioned to its original level with no discernible effect on the concrete posts. After several days of freezing overnight temperatures the loaded structure was still stable. Next a 4WD Jeep was chained to an end post of the 1-ton-loaded trellis with a strain gauge affixed in-line. It was necessary to load the vehicle with fifteen bags of 80# concrete (1200 lbs) to get sufficient traction to achieve a 4-ton co-liner load. After several such tests the trellis posts deflected less than 1-inch, but returned to plumb each time the load was removed. Finally, a 2-ton come-along was attached to the middle of the hi-tensile trellis wire and tensioned perpendicular to the simultaneously applied 4-ton collinear load.

    Unfortunately at almost 4-inches, well before the planned 10-inch deflection was reached, the two adjacent line posts (anchored only in tamped clay) were pulled from the ground, but the end posts (embedded in concrete) returned to plumb when all loading was removed. A recalculation of 80 mph wind loading as applied to a fully leafed-out canopy showed that the planned 10-inch deflection of the original (incorrect) computation was off by a factor of 10, meaning that only a 1-inch perpendicular deflection should have been used. Clearly the 120-foot-long trellis constructed with concrete posts and hi-tensile wire far exceeds all extreme loading conditions even including a once-in-twenty-five-year-expected-wind event.

    Cost Comparison:
    Concrete ready-mix 80# bags were purchased at $2.92 in pallet quantities. Half-inch rebar lengths of 10’ were discounted to $3.43 each. At these prices, the material cost of concrete posts spaced thirty feet apart for a 120-foot long trellis row is $34.67 (2 end posts @ $7.81 each and 3 line posts @ $6.35 each). The equivalent row of treated posts at 12’ spacing (recommended) is $72.47 (2, 5” end posts @ $8.74 each and 9, 4” line posts @ $6.11). Even at the maximum (not recommended) post spacing of 24’, the row cost is $48. Thus, if winter-time labor is not factored-in with material cost at the family farm, the homemade concrete post is a clear winner. For the recommended post spacings of 12’ for 4-5” diameter wooden posts vs. 30’ for the much stronger concrete posts, a material cost savings of $2,117 per acre should be realized.

    CONCLUSION
    The project was completely successful, fully meeting and exceeding all proposal goals. Based on material cost alone, the concrete post is clearly superior over treated wood posts. Additional advantages of concrete over wood include its strength, durability, simple wire-to-post fastening, ease of wire re-positioning, fewer posts required per trellis row, and concrete material impervious to lightning, fire, rot, and wood-boring insects.

    PROJECT IMPACTS
    As outlined on both the accompanying Benefits and Impacts form and the Grant Evaluation form, the use of sustainable concrete posts for trellising and fencing is economically and environmentally beneficial.

    OUTREACH
    1. The concrete post trellising system drew many ad hoc visitors to the vineyard. Invariably they would try to shake the posts and pull on the wires to check the tension. The very minimal skepticism always turned into excitement as the relative benefits especially that of cost savings were spelled out. The project was briefly announced at one seminar and several winegrower gatherings. The positive outcome of the project resulted in a second field day held at the vineyard.
    2. The first field day was attended by eight local farmers who were invited by phone and email. A second field day was announced by postings at two local feed stores and by word-of-mouth by project mentors, student workers, and neighbors having previously satisfied their curiosity by both casual and planned visits.
    3. Project results were presented at one workshop as well as at the two field days and on the project’s photo web site: http://sites.google.com/site/fnc2007684/.

    PROGRAM EVALUATION
    From this grant recipient’s perspective, all aspects of the NCR SARE Program are commendable. Especially of note is the helpful responsiveness of staff to questions.

    PROJECT EXPENDITURES
    This project was made possible by the combination of NCR-SARE grant funding ($4,300), student and part-time worker participation, in-kind labor, and cost overruns ($4,842) funded by the Ohio River Vista Vineyard and Research Station. The one fault was in the submitted project budget which underestimated material and labor costs. Cost over-run ($3,200) for hourly personnel was due to the underestimated amount of work hours in addition to an increased pay rate (from $10/hr to $15/hr.). Non-personnel cost over-run ($1,642) was mainly due to non-budgeted items such as the (unnecessary) pile driver rental, (necessary) powered augur rental, hi-tensile wire expense, and hand cart purchase. All cost over-runs were covered by ORVVWARS. In-kind labor contributions by major participants were voluntary.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.