Whenever I hear a fellow PhD student tell me that he/she has nothing to write a conference paper about, I get a little antsy.
While the main chunk of your research might not be ready yet, that doesn't mean you have nothing to show to the international research community in your field. Likewise, when your experiment is not finished yet, that doesn't mean you haven't learned something that isn't worth talking about.
When the purpose of your trip to a conference is to spark discussion, there are quite a number of topics that you can touch upon and use to your benefit to get early input from fellow researchers.
If you have travel budget, by all means, get your ass on a plane and go to as many conferences as you can. I truly think that my crazy conference schedule has been one of the key factors to my successful PhD.
Here are some examples of topics that you can write about early on and present at a conference:
1. Case study
Take an example from practice, and use the deeper knowledge that you obtained while making your literature review to delve into this case under consideration.
2. Review paper
A classic - but often overlooked type of paper. If you've spend the right energy in your literature review, you should be able to write great, critical review paper that other researchers in remotely connected fields would love to look at to learn more about your discipline.
3. Mix & Match paper
Why not compare the test results from research X with the theory from researcher Y? Play around with existing data, and see if you can learn something new from this. Doing so will only deepen your understanding of your topic.
4. Parameter study
Parameter studies can teach you a lot, and give you some good food to write about. Even simple Excel-style exercises to study how a certain parameter is represented in different theories and how this is observed in experiments will be a valuable starting point.
5. Bounds and Assumptions
If you've done your literature review correctly, you'll have identified the limitations and boundaries to the major existing theories in your field. You can use that insight and expand on it: what are the limiting assumptions and bounds of some of the most commonly used theories? What should we do as a research community to verify these bounds or to make sure the theory can include more exceptions?
6. Comparison of design methods
Maybe a typical idea for a structural engineering paper, but it's always interesting to compare different codes and design methods. Start with a simple case, and see what is the resulting design if you follow different codes. Make sure you discuss the boundaries and assumptions of the codes you considered.
7. Computer modeling
For reinforced concrete, computer modeling sure is a topic in itself that is worth a lot of advanced PhD research. However, you can always start modeling an experiment from the literature, and discuss your observations with respect to the different parameters that you need to assume. This technique will also give you the tools to model your own experiments more easily later on.
Do you feel inspired to go and tinker in the sideline and see what you can learn from these examples?