Concrete is a vastly misunderstood concept. It╒s goopy until it sets through a process of crystallization; it╒s stronger when mixed with a high proportion of cement (the glue); and its inherent brittleness can be reinforced with flexible materials. It can be poured into many molds, from short pieces of pipe to abandoned vehicles. You can buy the "quick-set" variety for rapid night work, but it╒s not as strong as the gradually curing kind (Portland cement) which you can mix at home for later deployment.
Chemistry Lesson
Cement develops its binding capacity through hydration as a result of a chemical reaction with water. "Portland" cement, the most commonly used to make concrete, consists of calcium silicates. Concrete has high compressive strength, but low tensile and flexural strength. This means only very hard blows will shatter concrete. Reinforcement (such as steel) can increase the overall strength of the product/form.
Cement, H2O, Sand and Stone
The best ratios to use are anywhere between 3:1:3:3 and 3:1:5:5 (cement:water:sand:gravel). The higher the proportions of sand and gravel, the weaker the end product will be. This is probably fine for road emplacements because weight is more important than compressive strength. Also, high cement-to-water ratios will make the concrete hard to stir, especially as you add more sand and gravel. You can up the water concentration to 2.5:1 (cement:water), however, this will increase the setting time. Rain water and snow melt are not recommended because they are very low in calcium. Tap and lake water are preferable. Sea water is usable, but will corrode steel reinforcement. Of the sands available, "plaster sand" works best because it contains lime (calcium) and has been screened to remove very fine particles. Gravel finer than 1/4 of an inch and greater than 1/16 of an inch in diameter is ideal for smaller objects (e.g., barrels), though larger sizes (up to 3/4 of an inch) can be used for very large emplacements (thousands of pounds). When you buy these components from outdoor yards, try to get the dry stuff from the top of the pile because absorbed water will screw up the above ratio estimates.
Three main kinds of cement are available: Portland cement types I, II and III. These set between 4,000 to 8,000 pounds per square inch (psi), depending on which type you use, how careful you are with ratios of cement to water and the setting time. Type III is the strongest and hardest to find (6,000 to 8,000 psi). Types I and II (4,000 to 6,000 psi) are usually used in sidewalks and are available at most large hardware stores. Adding commercial admixtures such as calcium chloride, granulated blast-furnace slag (type IS cement), and pozzolans (type IP cement) will give greater strength, sooner. Calcium aluminate (or high alumina) cement is 25 percent stronger than Portland and sets in a little over a day╒s time, even below freezing.
Storing, curing and temperature
The temptation with concrete is to try to use it as soon as possible after pouring. If you are using "quick-set," this is probably okay. However, as some people have found, regular concrete less than 24 hours old ain╒t worth shit. Plan ahead! Regular concrete has 75 percent of its ultimate strength after seven days and 99 percent of its ultimate strength after 28 days. Install road-embedded placements several weeks ahead of time, cover them up and come back later. Make barrels when nothing else is happening, not in the middle of a campaign. Make some in your garage and take them into the woods.
Concrete should be cured under humid conditions. Slop water on the top while it sets or put heavy absorbent materials soaked in water on top. This helps keep micro-cracks and larger cracks from forming. Air-cured concrete has 50 percent less compressive strength than moist-cured. While curing, concrete should not be exposed to extreme temperature changes. The warmer it is the better (70 to 100 degrees F). Though concrete will set at near freezing conditions, it will take longer and be weaker. Cure barrels and lockboxes in water and indoors, if possible.
Different Shapes
Obviously, the shape of the finished product will depend on the form (or mold) used to pour the concrete. The shape of the form will affect the strength of the object. Remember that concrete is brittle. Try to imagine where the force will be applied to break your barricade. With barrels, law enforcement officers often hammer at the sides to get at the lockbox inside. So, the more cylindrical the barrel is, the better, because the shock will be absorbed and dissipated effectively. Steel reinforcement will make concrete much harder to hammer through, but don╒t overdo it. Try to avoid thin layers of concrete and sharp corners. Concrete lockboxes are a relatively new approach worth pursuing. They are composed of a steel lockbox surrounded by a concrete sheath, enclosed within a 12-inch plastic form. Plan ahead so you don╒t have to use quick-set cement and remember to keep it moist.
Dragons and Other Fancy Stuff
If you are going to rely on road-embedded concrete to hold you down, it must be at least 50 percent cured. For regular concrete at spring road-bed temperatures (40 to 50 degrees Fahrenheit) this could take at least three days. Get out early to set up (like Friday night for a Monday action). Dig the hole, pour in several hundred pounds of concrete around your lockbox (or other locking devices, such as eye bolts), cover the concrete with something that can take a vehicle╒s weight (if autos will be going by in the daytime), cover with several inches of road material, pack it down well and mark the spot. After a long weekend, this will be strong enough to use. The deeper the plug, the deeper they╒ll have to dig to get it out. An easier way to do this is to take a pre-made barrel with a top- mounted lockbox and drop it into a ready-made hole. Someone once called a road emplacement like this a "sleeping dragon" because it can be activated whenever needed (weeks or years later).
History Lesson
A description from early 1994 for the Tacoma action barrels included information that is incorrect. Avoid the temptation to fill up space with extraneous materials like wood and big rocks. These objects will act as centers of chaos and autonomy within the barrel. Once hammering commences on the outside of the barrel, cracks will migrate between weak areas first. These are mostly the "transition zones" around wood or large rocks, air pockets, the lockbox, and even rebar reinforcement. So, keep that stuff to a bare minimum. Sidewalk-strength concrete will keep them hammering for awhile.
Barrel or Emplacement Design
For a 30-gallon barrel: 1) cut four-inch PVC or ABS pipe into two equal pieces that will join in the middle of the barrel to make a 150-degree angle "V"; 2) fit these through holes in the side of the barrel into a T-joint (flex tubing or PVC/ABS) which has a hole punched through the center with rebar; 3) heat the rebar (precut to 3 inches less than the height of the barrel) and push it through the hole in the T-joint; 4) cover the third open (vertical) side of the T-joint (a big yogurt lid will do); 5) put in a cage of reinforcing wire and rebar about 4 inches from the outside of the barrel, include cross pieces; 6) start mixing and pouring concrete (100 to 200 pounds a batch) until you fill it up (a 30-gallon barrel requires 600 pounds of concrete).
Remember: Scale the height of the holes in the side of the barrel to be comfortable for a seated person; keep the pipes secure while pouring the concrete; mix the concrete thoroughly to get rid of air bubbles and effectively mix in the cement paste.
Consider refrigerators, washing machines, old cars and custom made forms. If you decide to make something in the 1,000- to 3,000-pound class consider buying a half yard (1,500 pounds) or full yard (3,000 pounds) of concrete at a larger hardware store or concrete yard. If you do so, request that they add some extra cement to make it stronger. Pre-mixed concrete at this scale costs more but is a hell of a lot easier than the alternative. You will have to rent or know someone with a flat bed for this. Even one-ton pickups will die under this kind of load.
When delivering the finished product, try not to drop it off the truck. It will probably crack, especially if it is not completely set. Heavy timber ramps, big dollies and come- alongs will probably help. Avoid being downhill from said behemoth.
Say It With Concrete
With the above recipes, lots of imagination and a human or two who will never unlock, you can tie up traffic and law enforcement for several hours to several days. Dream about concrete lockboxes around truck axles, dragons awakening in the road, refrigerators full of sidewalk and full-leg enclosures in buried barrels.