CA3178337A1 - Method and mold for controlling for slump and bulge during manufacture of interlocking concrete retaining wall blocks - Google Patents

Description

Method and Mold For Controlling For Slump and Bulge During Manufacture of Interlocking Concrete Retaining Wall Blocks Description In a Dry-Cast concrete Mold, forming concrete blocks in a vertical or "Face-Up" fashion allows for the application of various textures and colours to the visible face of the product.
When a Mold is configured to manufacture blocks in a "Face-Up" fashion, the left and right sides to the Blocks are formed with fixed rigid sidewalls. This is shown in Figure 1.
When the blocks are placed or stacked in a Wall, they are rotated 90 degrees and the left/right sides of the block become the Top/Bottom of the Block. This is shown in Figure 2.
When stacking blocks as shown, it is critical that the vertical dimension at the front (X) and the rear (Y) of the block are identical. This is shown in Figure 3.
If these dimensions are not identical, even by very small amounts such as 2-3mm, the side profile of the block takes on a wedge shape as shown below (in this case Y >X). This is shown in Figure 4.
When this occurs, the Blocks will not be level and will cause the wall to rotate forward more with each stacked course. This makes the wall structurally unstable and visually unappealing. This is shown in Figure 5.
For structural purposes, these concrete blocks are often required to be at least 250-300mm in depth when placed in the wall. In the Mold, this "depth" is the height of the unit when made Face-Up as shown above. The process of Dry-Cast concrete forming has the benefit of very fast production of the molded units based on the using a low water content in the concrete mix and then removing the mold almost immediate after the concrete is filled, formed, and compacted. In a typical case, the concrete may only be in the mold 15-40 seconds before the mold is lifted and the "green" concrete units are left to stand freely on the production board without support.
This method of manufacturing was originally developed many years ago for Paving Stone and was adapted for larger retaining wall blocks overtime. As paving stones are relatively short (60-70mm typically), the Dry-Cast method works well, and the green concrete maintains its vertical alignment easily. As the Concrete Units become taller, with greater weight, even with a relatively Dry mixture, the units may undergo a certain amount of slump or widening at the bottom before the cement has a chance to set-up or cure on the board.
In current practice, the dry concrete mixture is placed into the Mold cavities and compacted under high pressure and vibration with Press Heads. This is shown in Figure 6.
After a cycle time of between 15-45 seconds typically, the mold is lifted upwards and the green concrete product remains on the production board. This is shown in Figure 7.
Depending on the mix design and height of the Concrete unit, the self-weight of the uncured concrete could cause some slumping or widening at the bottom. In the industry this is sometime referred to as "elephant feet", with the face dimension (X) being smaller than the back dimension (Y>X). This is shown in Figure 8.
Date Regue/Date Received 2022-10-04 Furthermore, if additional geometry is required in the Block to facilitate an interlock between units (used for vertical alignment to create a set wall batter or lean and also for interblock Shear Strength in the Wall), a different phenomenon occurs which can also lead to bulging in the bottom of the Unit. To create an interlocking geometry in the block, undercuts are required as shown below. As these undercuts are off-plane with the sidewalls, they would interfere with the mold being vertically ejected.
As such, removable Draw Fingers are required which are compatible with the interior sidewalls and slide in and out of the Mold (A). This is shown in Figure 9.
After the Mold is filled, there is tremendous compaction/vibration pressure applied to the concrete mixture. As these forces are contained, they build up within the cavities. The sequence for removing the Mold when using Draw Fingers is to first remove the Draw Fingers, then lift the mold.
When the Draw Fingers are removed very rapidly, before the Mold Sidewalls are lifted, there is a release of these Compaction stresses in the area where the Draw Fingers once were.
This is shown in Figure 10.
These forces would be the highest in the direction perpendicular to the vertical sidewall and lowest as they radiate toward the bottom of the block (the production board) as this is supported.
As a result of this release of pressures within the cavity, trials have shown that a bulge was created in the area closest to the interface between the Fixed Interior Wall and the Draw Finger on both sides of the product. This is shown in Figure 11.
This bulge released the stresses and pressure that built up during compaction, however, it resulted in blocks that did not bear flat or level when stacked. This is shown in Figure 12.
It is an object of this description to obviate or mitigate the above-noted deficiencies.
To solve this issue and combat the bulging and slumping effect discussed above, a specially designed female arch was introduced into the Draw Finger Geometry at very specific locations. We will refer to this as the Pressure Dissolution Arch (PDA).
In the embodiment provided, we have a Male Rear Interlock Lip and a Female Rear Interlock notch.
For the Male interlock Lip, the PDA is placed at the highest point in the Draw Finger just in front of the Rear Lip. As a result, we have to increase the height of the Draw Fingers to position the PDA
immediately in front of the critical zone (where the Male/Female interlock align when stacked).
We have determined that approximately 2-5mm of bulge is possible and therefore, the PDA is designed with compatible dimensions to ensure this area still remains out of the plane of influence between the top/bottom surfaces. This is shown in Figure 13.
The PDA works in two ways. First, the Arch naturally has certain amount of strength through its inherent geometry to distribute the residual compaction forces/stresses along its length and dissipate them into the abutting volumes of concrete, versus directly "out" or perpendicular to the vertical face.
This is shown in Figure 14.
Second, if the Arch does collapse under the pressure, the negative volume that exists is sufficient to allow a certain amount of bulging without it crossing the vertical plane and interfering with the placement of the units. This is shown in Figure 15.
Date Regue/Date Received 2022-10-04 For the female Notch, the optimum position for the PDA is the highest position immediately behind the interlocking slope. This is shown in Figure 16.
The resulting configuration for the Draw Fingers would be as shown in Figure 17.
Full scale testing has shown that the PDA on either side of the unit also allows a path for potential slump in the product to move, which ultimately has solved both problems.
Date Regue/Date Received 2022-10-04