I have a 25 year old concrete patio next to my concrete inground swimming pool. The 2 x 4's imbetween the slabs have rotted away and the space between the slabs is empty except for dirt and weeds. The slabs are lopsided but not bad. I want to fill the space between the slabs but do not want to use 2x4's. (I don't think I could make them fit, for I have no tools and would not be able to move or lift the concrete slabs.) Is there a way of doing this? The reason is when I walk or sit on the concrete area I am always tripping or stepping into the empty space. I would like to find a solution that is economical and does not take too much talent. I know the material I use must be pliable because the space is for expansion of the concrete due to weather conditions.