There are two well-known ways to model the curing of concrete in Microsoft Project. But both ways may generate critical path discontinuities is certain situations.
The first way to model the concrete cure time in Microsoft Project is as an elapsed time lag. This works well to model the continuous nature of concrete curing through the weekends. The drawback of this approach, however, is a lack of visibility. The reason for the lag delay is not apparent in the task table or on the Gantt chart.
This negative has led to another popular approach for modeling the cure time of concrete that also includes weekend cure. In this method the cure time is modeled as an actual task with a seven day workweek schedule calendar. As this task does not require human effort no resources are assigned, and this makes the task somewhat unique. What is beneficial to this concrete cure modeling approach is that the task clearly documents the effort, concrete curing.
Never-the-less both approaches create critical path breaks in certain situations. One of the characteristics of a quality schedule is a continuous critical path that has no discontinuities, so critical path breaks are a problem.
This article discusses a quick tip to address schedule discontinuities that may occur when modeling the cure time of concrete in Microsoft Project.
Our first demonstration project is displayed in Figure 1.
This is a pipe repair and improvement project. Note, in particular, the lag after pour concrete. This is a 6-day elapsed time lag (6ed), Figure 2, which models the curing of concrete through the weekends.
The concrete takes six days to cure. Watch what happen when the concrete only takes 3-days to cure, Figure 3.
Our critical path breaks, Figure 4.
This is not good! Multi-hundred Million dollar projects have been placed on hold because of a critical path discontinuity. How do we rectify this situation?
The best approach in Microsoft Project is to simply update the definition of critical tasks. This is done by first selecting File | Options, Figure 5.
Currently tasks are critical if slack is less than or equal to 0 days, Figure 6.
Let’s update this definition to account for our 3-day weekend, Figure 7.
We make critical activities three days or less. The resulting schedule is displayed in Figure 8.
We have regained our continuous critical path, which is good.
Our second demonstration project displays in Figure 9.
This time the curing of concrete is modeled as a task and not a lag. Again, watch what happens when the cure concrete task is 3-days, Figure 10.
We, again, lose our continuous critical path, which is disconcerting. The best way to address this issue in Microsoft Project is, again, to update our critical task definition to account for the 3-day weekends, Figure 11.
Again, we make critical tasks three days or less. The final schedule is displayed in Figure 12.
Despite the 3-days total slack on some tasks the critical path remains continuous.
When modeling the curing of concrete through weekends there are situations when the concrete cure duration creates positive total slack. This causes a discontinuity in the schedule, which is a problem. This issue arises on a 5-day work week when the curing completes on Friday. If this is your situation then you should make the definition of critical tasks 2 days or less.
You may want to additionally make the definition of critical tasks 3 days or less to account for Monday holidays. As demonstrated, this complication also occurs on a 4-day work week when the curing completes on Thursday. For this situation make the definition of critical tasks 3 days or less. Similarly, you may want to make the definition of critical tasks 4 days or less, again, to account for Monday holidays.
So it is possible to model concrete cure in Microsoft Project while avoiding critical path breaks. Make sure to document your definition of critical tasks in memorandums associated with your project schedule.